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'''Sialyl Lewis<sup>X</sup> (sLeX)''', also known as '''cluster of differentiation 15s''' ('''CD15s''') or '''stage-specific embryonic antigen 1''' ('''SSEA-1'''), is a tetrasaccharide [[carbohydrate]] which is usually attached to O-[[glycans]] on the surface of cells. It is known to play a vital role in cell-to-cell recognition processes. It is also the means by which an egg attracts sperm; first, to stick to it, then bond with it and eventually form a zygote.
'''Sialyl Lewis<sup>X</sup> (sLeX)''', also known as '''cluster of differentiation 15s''' ('''CD15s''') or '''stage-specific embryonic antigen 1''' ('''SSEA-1'''), is a tetrasaccharide [[carbohydrate]] which is usually attached to O-[[glycans]] on the surface of cells. It is known to play a vital role in cell-to-cell recognition processes. It is also the means by which an egg attracts sperm; first, to stick to it, then bond with it and eventually form a zygote.


Sialyl Lewis <sup>X</sup> is also one of the most important [[Lewis antigen system|blood group antigens]] and is displayed on the terminus of glycolipids that are present on the cell surface. The sialyl Lewis <sup>X</sup> determinant, E-[[selectin]] ligand carbohydrate structure, is constitutively expressed on [[granulocyte]]s and [[monocyte]]s and mediates inflammatory extravasation of these cells. Resting [[T cell|T]]- and [[B cell|B]]-[[lymphocyte]]s lack its expression and are induced to strongly express sialyl Lewis <sup>X</sup> upon activation. The sialyl Lewis <sup>X</sup> determinant is expressed preferentially on activated [[Th1 cell]]s but not on [[Th2 cell]]s.
Sialyl-Lewis<sup>X</sup> is also one of the most important [[Lewis antigen system|blood group antigens]] and is displayed on the terminus of glycolipids that are present on the cell surface. The sialyl-Lewis<sup>X</sup> determinant, E-[[selectin]] ligand carbohydrate structure, is constitutively expressed on [[granulocyte]]s and [[monocyte]]s and mediates inflammatory extravasation of these cells. Resting [[T cell|T]] and [[B cell|B]] [[lymphocyte]]s lack its expression and are induced to strongly express sialyl-Lewis<sup>X</sup> upon activation. The sialyl-Lewis<sup>X</sup> determinant is expressed preferentially on activated [[Th1 cell|T<sub>h</sub>1 cell]]s but not on [[Th2 cell|T<sub>h</sub>2 cell]]s.


==Structure==
==Structure==
Sialyl-Lewis X is a tetrasaccharide composed of a [[sialic acid]], [[fucose]] and an [[N-acetyllactosamine]]. Its systematic name is 5-acetylneuraminyl-(2-3)-galactosyl-(1-4)-(fucopyranosyl-(1-3))-N-acetylglucosamine (Neu5Acα2-3Galβ1-4[Fucα1-3]GlcNAcβ). In humans, according to Table 1<ref>{{Cite journal|last1=de Vries|first1=T.|last2=Knegtel|first2=R. M.|last3=Holmes|first3=E. H.|last4=Macher|first4=B. A.|date=October 2001|title=Fucosyltransferases: structure/function studies|journal=Glycobiology|volume=11|issue=10|pages=119R–128R|doi=10.1093/glycob/11.10.119r|issn=0959-6658|pmid=11588153|doi-access=free}}</ref> and Fig.1<ref name=":0">{{Cite journal|last1=Trinchera|first1=Marco|last2=Aronica|first2=Adele|last3=Dall’Olio|first3=Fabio|date=2017-02-23|title=Selectin Ligands Sialyl-Lewis a and Sialyl-Lewis x in Gastrointestinal Cancers|journal=Biology|volume=6|issue=1|pages=16|doi=10.3390/biology6010016|issn=2079-7737|pmc=5372009|pmid=28241499|doi-access=free}}</ref> it is synthesized by four [[fucosyltransferase]]s: [[Fucosyltransferase 3|FUT3]], [[FUT5]], [[FUT6]] and [[FUT7]]. The other three enzymes of the [[sialyltransferase]] family [[ST3GAL3]], [[ST3GAL4]], and [https://www.ncbi.nlm.nih.gov/gene/10402 ST3GAL6] participate in the synthesis of the Sialyl-Lewis <sup>X</sup> precursor.<ref name=":0" />
Sialyl-Lewis<sup>X</sup> is a tetrasaccharide composed of a [[sialic acid]], [[fucose]] and an [[N-acetyllactosamine|''N''-acetyllactosamine]]. Its systematic name is 5-acetylneuraminyl-(2-3)-galactosyl-(1-4)-(fucopyranosyl-(1-3))-''N''-acetylglucosamine (Neu5Acα2-3Galβ1-4[Fucα1-3]GlcNAcβ). In humans,<ref>{{Cite journal|last1=de Vries|first1=T.|last2=Knegtel|first2=R. M.|last3=Holmes|first3=E. H.|last4=Macher|first4=B. A.|date=October 2001|title=Fucosyltransferases: structure/function studies|journal=Glycobiology|volume=11|issue=10|pages=119R–128R|doi=10.1093/glycob/11.10.119r|issn=0959-6658|pmid=11588153|doi-access=free}}</ref><ref name=":0">{{Cite journal|last1=Trinchera|first1=Marco|last2=Aronica|first2=Adele|last3=Dall’Olio|first3=Fabio|date=2017-02-23|title=Selectin Ligands Sialyl-Lewis a and Sialyl-Lewis x in Gastrointestinal Cancers|journal=Biology|volume=6|issue=1|pages=16|doi=10.3390/biology6010016|issn=2079-7737|pmc=5372009|pmid=28241499|doi-access=free}}</ref> it is synthesized by four [[fucosyltransferase]]s: [[Fucosyltransferase 3|FUT3]], [[FUT5]], [[FUT6]] and [[FUT7]]. The other three enzymes of the [[sialyltransferase]] family, [[ST3GAL3]], [[ST3GAL4]], and [[ST3GAL6]], participate in the synthesis of the sialyl-Lewis<sup>X</sup> precursor.<ref name=":0" />


==Function==
==Function==
===Leukocyte homing===
===Leukocyte homing===
Sialyl-Lewis<sup>x</sup> is important in leukocyte tethering and rolling. Leukocytes move through the blood stream and then tether themselves to the endothelial wall and roll along the endothelial tissue to determine if they want to leave the bloodstream to get to necessary tissue. Sialyl-Lewis<sup>x</sup> is a necessary partner for the three selectins that bind the leukocyte and endothelial cells. When sialyl-Lewis<sup>x</sup> is part of an O-glycan and attached to CD34 it can then bind to L-selectin. For the binding to L-selectin to occur sialyl-Lewis<sup>x</sup> must undergo sulfation. For sialyl-Lewis<sup>x</sup> to bind to P-selectin, an O-linked glycan near the N-terminus of P-Selectin Glycoprotein Ligand-1 (PSGL-1) is modified with sialyl-Lewis<sup>x</sup> and in combination with nearby tyrosine residues modified with sulfate, forms the binding contact for P-selectin. For sialyl-Lewis<sup>x</sup> to bind to E-selectin it can be part of either an N-linked or O-linked glycan attached to cell surface glycoproteins such as PSGL-1, CD43 or CD44. This sialyl-Lewis<sup>x</sup> mediated binding to selectins allows circulating leukocytes to stick to and roll along endothelial cells lining blood vessels thereby enabling the leukocytes to accumulate at a site of vascular inflammation.
Sialyl-Lewis<sup>X</sup> is important in leukocyte tethering and rolling. Leukocytes move through the blood stream and then tether themselves to the endothelial wall and roll along the endothelium before potentially exiting into the tissue. Sialyl-Lewis<sup>X</sup> is a necessary partner for the three selectins that bind the leukocyte and endothelial cells. When sialyl-Lewis<sup>X</sup> is part of an O-glycan and attached to CD34, it can then bind to L-selectin. For the binding to L-selectin to occur, sialyl-Lewis<sup>X</sup> must undergo sulfation. For sialyl-Lewis<sup>X</sup> to bind to P-selectin, an O-linked glycan near the N-terminus of P-selectin glycoprotein ligand-1 (PSGL-1) is modified with sialyl-Lewis<sup>X</sup> and, in combination with nearby tyrosine residues modified with sulfate, forms the binding contact for P-selectin. For sialyl-Lewis<sup>X</sup> to bind to E-selectin, it can be part of either an N-linked or O-linked glycan attached to cell surface glycoproteins such as PSGL-1, CD43 or CD44. This sialyl-Lewis<sup>X</sup>-mediated binding to selectins allows circulating leukocytes to stick to and roll along endothelial cells lining blood vessels, thereby enabling the leukocytes to accumulate at a site of vascular inflammation.


===Fertilization===
===Fertilization===
Sialyl-Lewis<sup>x</sup> allows a sperm cell to recognize and fertilize an egg cell. For fertilization to occur, human sperm must bind to the [[zona pellucida]] (ZP), the translucent matrix covering the human egg composed of four glycoproteins ZP1, 2, 3, and 4, and transit through the matrix in order to fuse with the oocyte.<ref>{{Cite journal | last1 = Clark | first1 = G. F. | title = The role of carbohydrate recognition during human sperm-egg binding | doi = 10.1093/humrep/des447 | journal = Human Reproduction | volume = 28 | issue = 3 | pages = 566–577 | year = 2013 | pmid = 23315069| doi-access = free }}</ref> Human ZP is coated with highly dense N- and O-glycans that are terminated with the sialyl-Lewis<sup>x</sup> sequence.<ref name="Pang">{{cite journal |last1=Pang |first1=Poh-Choo |last2=Chiu |first2=Philip C. N. |last3=Lee |first3=Cheuk-Lun |last4=Chang |first4=Lan-Yi |last5=Panico |first5=Maria |last6=Morris |first6=Howard R. |last7=Haslam |first7=Stuart M. |last8=Khoo |first8=Kay-Hooi |last9=Clark |first9=Gary F. |last10=Yeung |first10=William S. B. |last11=Dell |first11=Anne |display-authors=2 |date=18 August 2011 |title=Human Sperm Binding Is Mediated by the Sialyl-Lewisx Oligosaccharide on the Zona Pellucida |journal=Science |volume=333 |issue=6050 |pages=1761–1764 |bibcode=2011Sci...333.1761P |doi=10.1126/science.1207438 |pmid=21852454 |s2cid=23610213 |hdl-access=free |hdl=10044/1/15584}}</ref> The hemizona assay, which assesses sperm-ZP binding by counting the number of sperm bound to hemispheres of bisected nonliving human eggs ''in vitro'', revealed that as little as 0.5 mM sialyl-Lewis<sup>x</sup> inhibits sperm-ZP binding by 63%.<ref name="Pang" /> Furthermore, adding purified and solubilized ZP3 or ZP4 from the human oocyte dose-dependently inhibits sperm-ZP binding in the hemizona assay.<ref>{{Cite journal | last1 = Chiu | first1 = P. C. N. | last2 = Wong | first2 = B. S. T. | last3 = Chung | first3 = M. -K. | last4 = Lam | first4 = K. K. W. | last5 = Pang | first5 = R. T. K. | last6 = Lee | first6 = K. -F. | last7 = Sumitro | first7 = S. B. | last8 = Gupta | first8 = S. K. | last9 = Yeung | first9 = W. S. B. | doi = 10.1095/biolreprod.108.069344 | title = Effects of Native Human Zona Pellucida Glycoproteins 3 and 4 on Acrosome Reaction and Zona Pellucida Binding of Human Spermatozoa | journal = Biology of Reproduction | volume = 79 | issue = 5 | pages = 869–877 | year = 2008 | pmid = 18667750| doi-access = free }}</ref> Such evidence suggest that the early steps of human sperm-egg binding may be mediated by lectins for sialyl-Lewis<sup>x</sup> present on human sperm.
Sialyl-Lewis<sup>X</sup> allows a sperm cell to recognize and fertilize an egg cell. For fertilization to occur, human sperm must bind to the [[zona pellucida]] (ZP), the translucent matrix covering the human egg composed of four glycoproteins—ZP1, 2, 3, and 4—and transit through the matrix in order to fuse with the oocyte.<ref>{{Cite journal | last1 = Clark | first1 = G. F. | title = The role of carbohydrate recognition during human sperm-egg binding | doi = 10.1093/humrep/des447 | journal = Human Reproduction | volume = 28 | issue = 3 | pages = 566–577 | year = 2013 | pmid = 23315069| doi-access = free }}</ref> The human ZP is coated with dense N- and O-glycans that are terminated with the sialyl-Lewis<sup>X</sup> sequence.<ref name="Pang">{{cite journal |last1=Pang |first1=Poh-Choo |last2=Chiu |first2=Philip C. N. |last3=Lee |first3=Cheuk-Lun |last4=Chang |first4=Lan-Yi |last5=Panico |first5=Maria |last6=Morris |first6=Howard R. |last7=Haslam |first7=Stuart M. |last8=Khoo |first8=Kay-Hooi |last9=Clark |first9=Gary F. |last10=Yeung |first10=William S. B. |last11=Dell |first11=Anne |display-authors=2 |date=18 August 2011 |title=Human Sperm Binding Is Mediated by the Sialyl-Lewisx Oligosaccharide on the Zona Pellucida |journal=Science |volume=333 |issue=6050 |pages=1761–1764 |bibcode=2011Sci...333.1761P |doi=10.1126/science.1207438 |pmid=21852454 |s2cid=23610213 |hdl-access=free |hdl=10044/1/15584}}</ref> The hemizona assay, which assesses sperm–ZP binding by counting the number of sperm bound to hemispheres of bisected nonliving human eggs ''in vitro'', reveals that 0.5 mM sialyl-Lewis<sup>X</sup> inhibits sperm–ZP binding by 63%.<ref name="Pang" /> Furthermore, adding purified and solubilized ZP3 or ZP4 from the human oocyte dose-dependently inhibits sperm–ZP binding in the hemizona assay.<ref>{{Cite journal | last1 = Chiu | first1 = P. C. N. | last2 = Wong | first2 = B. S. T. | last3 = Chung | first3 = M. -K. | last4 = Lam | first4 = K. K. W. | last5 = Pang | first5 = R. T. K. | last6 = Lee | first6 = K. -F. | last7 = Sumitro | first7 = S. B. | last8 = Gupta | first8 = S. K. | last9 = Yeung | first9 = W. S. B. | doi = 10.1095/biolreprod.108.069344 | title = Effects of Native Human Zona Pellucida Glycoproteins 3 and 4 on Acrosome Reaction and Zona Pellucida Binding of Human Spermatozoa | journal = Biology of Reproduction | volume = 79 | issue = 5 | pages = 869–877 | year = 2008 | pmid = 18667750| doi-access = free }}</ref> Such evidence suggest that the early steps of human sperm–egg binding may be mediated by lectins for sialyl-Lewis<sup>X</sup> present on human sperm.


==Clinical significance==
==Clinical significance==
===Leukocyte adhesion deficiency===
===Leukocyte adhesion deficiency===
{{Main|Congenital disorder of glycosylation type IIc}}
{{Main|Congenital disorder of glycosylation type IIc}}
Defective synthesis of the sialyl Lewis <sup>X</sup> antigen results in immunodeficiency ([[leukocyte adhesion deficiency]] type 2). Defective synthesis can be caused by the loss of fucosyltransferase, impairing the glycosylation of the glycosphingolipid. Sialyl Lewis x is being researched for detection and treatment of immune disorders because of its presence on leukocytes.
Defective synthesis of the sialyl-Lewis<sup>X</sup> antigen results in immunodeficiency ([[leukocyte adhesion deficiency]] type 2). Defective synthesis can be caused by the loss of fucosyltransferase, impairing the glycosylation of the glycosphingolipid. Sialyl-Lewis<sup>X</sup> is being researched for detection and treatment of immune disorders because of its presence on leukocytes.


===Blood cancers===
===Blood cancers===
Sialyl-Lewis<sup>x</sup> mediates [[phagocytosis]] and [[chemotaxis]], found on neutrophils;<ref name="pmid1362195">{{cite journal |vauthors=Kerr MA, Stocks SC | title = The role of CD15-(Le(X))-related carbohydrates in neutrophil adhesion | journal = Histochem. J. | volume = 24 | issue = 11 | pages = 811–26 |date=November 1992 | pmid = 1362195 | doi = 10.1007/BF01046353| s2cid = 8602651 }}</ref> expressed in patients with Hodgkin disease, some B-cell chronic lymphocytic leukemias, acute lymphoblastic leukemias, and most acute nonlymphocytic leukemias. CD15 is present on almost all [[Reed–Sternberg cell]]s, including their rare mononuclear variants, and, as such, can be used in [[immunohistochemistry]] to identify the presence of such cells in biopsies. The presence of these cells is diagnostic of [[Hodgkin's lymphoma]]. Reed-Sternberg cells display a characteristic pattern of Sialyl-Lewis<sup>x</sup> (CD15) positivity, with membranous staining combined with staining of the [[Golgi apparatus]]. Immunohistochemical panels for the diagnosis of Hodgkins disease typically employ CD15 along with [[CD30]] and [[CD45]]; the latter does not stain Reed-Sternberg cells, but does stain almost all other lymphoid cells. Sialyl-Lewis<sup>x</sup> is also present in about 50% of [[adenocarcinoma]] cells and can be used to distinguish such conditions from [[mesothelioma]], which is typically negative.<ref name=Leong>{{cite book|author=Leong, Anthony S-Y|author2=Cooper, Kumarason|author3=Leong, F Joel W-M|year=2003|title=Manual of Diagnostic Cytology|edition=2nd|publisher=Greenwich Medical Media, Ltd.|pages=83–84|isbn=1-84110-100-1}}</ref>
Sialyl-Lewis<sup>X</sup> mediates [[phagocytosis]] and [[chemotaxis]], found in neutrophils;<ref name="pmid1362195">{{cite journal |vauthors=Kerr MA, Stocks SC | title = The role of CD15-(Le(X))-related carbohydrates in neutrophil adhesion | journal = Histochem. J. | volume = 24 | issue = 11 | pages = 811–26 |date=November 1992 | pmid = 1362195 | doi = 10.1007/BF01046353| s2cid = 8602651 }}</ref> it is expressed by cells present in Hodgkin disease, some B-cell chronic lymphocytic leukemias, acute lymphoblastic leukemias, and most acute nonlymphocytic leukemias. CD15 is present on almost all [[Reed–Sternberg cell]]s, including their rare mononuclear variants, and, as such, can be used in [[immunohistochemistry]] to identify the presence of such cells in biopsies. The presence of these cells is diagnostic of [[Hodgkin's lymphoma]]. Reed–Sternberg cells display a characteristic pattern of sialyl-Lewis<sup>X</sup> positivity, with membranous staining combined with staining of the [[Golgi apparatus]]. Immunohistochemical panels for the diagnosis of Hodgkin's disease typically employ CD15 along with [[CD30]] and [[CD45]]; the latter does not stain Reed–Sternberg cells, but does stain almost all other lymphoid cells. Sialyl-Lewis<sup>X</sup> is also present in about 50% of [[adenocarcinoma]] cells and can be used to distinguish such conditions from [[mesothelioma]], which is typically negative.<ref name=Leong>{{cite book|author=Leong, Anthony S-Y|author2=Cooper, Kumarason|author3=Leong, F Joel W-M|year=2003|title=Manual of Diagnostic Cytology|edition=2nd|publisher=Greenwich Medical Media, Ltd.|pages=83–84|isbn=1-84110-100-1}}</ref>


===Cancer metastasis===
===Cancer metastasis===
Sialyl-Lewis<sup>x</sup> plays a critical role in cancer metastasis, facilitating the extravasation of cancer cells out of the bloodstream while they are moving through the body. Its expression is related to tumor stage, recurrence, and overall patient survival.<ref>{{Cite journal|last1=Liang|first1=Jin-xiao|last2=Liang|first2=Yong|last3=Gao|first3=Wei|date=2016-05-24|title=Clinicopathological and prognostic significance of sialyl Lewis X overexpression in patients with cancer: a meta-analysis|journal=OncoTargets and Therapy|volume=9|pages=3113–3125|doi=10.2147/OTT.S102389|issn=1178-6930|pmc=4888715|pmid=27307752 |doi-access=free }}</ref> Therefore, sialyl Lewis x is being used as a target in studies to fight tumors and cancer cell growth. It has been shown that there is frequent overexpression of sialyl Lewis x on cancer cells and is found on both N-glycan and O-glycans. Sialyl Lewis x is being researched with CD markers to find new ways to create biosensors for cancer cells. Also, it is being used in new ways to target cancer cells specifically for cancer treatment.
Sialyl-Lewis<sup>X</sup> plays a critical role in cancer metastasis, facilitating the extravasation of cancer cells out of the bloodstream when they are moving through the body. Its expression is related to tumor stage, recurrence, and overall patient survival.<ref>{{Cite journal|last1=Liang|first1=Jin-xiao|last2=Liang|first2=Yong|last3=Gao|first3=Wei|date=2016-05-24|title=Clinicopathological and prognostic significance of sialyl Lewis X overexpression in patients with cancer: a meta-analysis|journal=OncoTargets and Therapy|volume=9|pages=3113–3125|doi=10.2147/OTT.S102389|issn=1178-6930|pmc=4888715|pmid=27307752 |doi-access=free }}</ref> Therefore, sialyl Lewis x is being used as a target in studies to fight tumors and cancer cell growth. There is frequent overexpression of sialyl-Lewis<sup>X</sup> on cancer cells, and it is found on both N-glycan and O-glycans. Sialyl-Lewis<sup>X</sup> is being researched with CD markers to find new ways to create biosensors for cancer cells. It is also being used in new ways to target cancer cells specifically for cancer treatment.


===In vitro fertilization===
===In vitro fertilization===
{{further|In vitro fertilization}}
{{further|In vitro fertilization}}
Sialyl-Lewis<sup>x</sup> is being used to achieve greater rates of fertilization of eggs in women by coating the eggs with sialyl Lewis x.
Sialyl-Lewis<sup>X</sup> is being used to achieve greater rates of fertilization of eggs in women by coating the eggs with sialyl-Lewis<sup>X</sup>.


===Immunity and inflammation===
===Immunity and inflammation===
It plays a key role in the inflammatory response and may be used to increase the leukocyte response to infections. Sialyl Lewis x is also an inflammation-associated antigen on liver cells. It becomes over expressed on diseased liver cells and can be used as a way to detect liver disease in a patient.
Sialyl-Lewis<sup>X</sup> plays a key role in the inflammatory response and may be used to increase the leukocyte response to infections. Sialyl-Lewis<sup>X</sup> is also an inflammation-associated antigen on liver cells. It is overexpressed on diseased liver cells and can be used as a way to detect liver disease in a patient.


===MERS coronavirus binding===
===MERS coronavirus binding===
In June 2019, before the onset of the [[COVID-19 pandemic]], the sulfated sialyl-Lewis X oligosaccharide (particularly with α2,3 linkages) receptor was found to be the preferred binding site, both in humans and in dromedary camels, for the coronavirus causing Middle East Respiratory Syndrome ([[MERS]]), the sixth coronavirus to be described.<ref>{{cite journal |last1=Tortorici |first1=M. Alejandra |last2=Walls |first2=Alexandra C. |last3=Lang |first3=Yifei |last4=Wang |first4=Chunyan |last5=Li |first5=Zeshi |last6=Koerhuis |first6=Danielle |last7=Boons |first7=Geert-Jan |last8=Bosch |first8=Berend-Jan |last9=Rey |first9=Félix A. |last10=de Groot |first10=Raoul J. |last11=Veesler |first11=David |title=Structural basis for human coronavirus attachment to sialic acid receptors |journal=Nature Structural & Molecular Biology |date=June 2019 |volume=26 |issue=6 |pages=481–489 |doi=10.1038/s41594-019-0233-y |pmid=31160783 |pmc=6554059 }}</ref><ref>{{cite journal |last1=Li |first1=Wentao |last2=Hulswit |first2=Ruben J. G. |last3=Widjaja |first3=Ivy |last4=Raj |first4=V. Stalin |last5=McBride |first5=Ryan |last6=Peng |first6=Wenjie |last7=Widagdo |first7=W. |last8=Tortorici |first8=M. Alejandra |last9=Dieren |first9=Brenda van |last10=Lang |first10=Yifei |last11=Lent |first11=Jan W. M. van |last12=Paulson |first12=James C. |last13=Haan |first13=Cornelis A. M. de |last14=Groot |first14=Raoul J. de |last15=Kuppeveld |first15=Frank J. M. van |last16=Haagmans |first16=Bart L. |last17=Bosch |first17=Berend-Jan |title=Identification of sialic acid-binding function for the Middle East respiratory syndrome coronavirus spike glycoprotein |journal=Proceedings of the National Academy of Sciences |date=3 October 2017 |volume=114 |issue=40 |pages=E8508–E8517 |doi=10.1073/pnas.1712592114 |pmid=28923942 |pmc=5635925 |bibcode=2017PNAS..114E8508L |s2cid=20912646 |doi-access=free }}</ref>
In June 2019, before the onset of the [[COVID-19 pandemic]], the receptor for sulfated sialyl-Lewis<sup>X</sup> oligosaccharide (particularly with α2,3 linkages) was found to be the preferred binding site, both in humans and in dromedary camels, for the coronavirus causing Middle East respiratory syndrome ([[MERS]]), the sixth coronavirus to be described.<ref>{{cite journal |last1=Tortorici |first1=M. Alejandra |last2=Walls |first2=Alexandra C. |last3=Lang |first3=Yifei |last4=Wang |first4=Chunyan |last5=Li |first5=Zeshi |last6=Koerhuis |first6=Danielle |last7=Boons |first7=Geert-Jan |last8=Bosch |first8=Berend-Jan |last9=Rey |first9=Félix A. |last10=de Groot |first10=Raoul J. |last11=Veesler |first11=David |title=Structural basis for human coronavirus attachment to sialic acid receptors |journal=Nature Structural & Molecular Biology |date=June 2019 |volume=26 |issue=6 |pages=481–489 |doi=10.1038/s41594-019-0233-y |pmid=31160783 |pmc=6554059 }}</ref><ref>{{cite journal |last1=Li |first1=Wentao |last2=Hulswit |first2=Ruben J. G. |last3=Widjaja |first3=Ivy |last4=Raj |first4=V. Stalin |last5=McBride |first5=Ryan |last6=Peng |first6=Wenjie |last7=Widagdo |first7=W. |last8=Tortorici |first8=M. Alejandra |last9=Dieren |first9=Brenda van |last10=Lang |first10=Yifei |last11=Lent |first11=Jan W. M. van |last12=Paulson |first12=James C. |last13=Haan |first13=Cornelis A. M. de |last14=Groot |first14=Raoul J. de |last15=Kuppeveld |first15=Frank J. M. van |last16=Haagmans |first16=Bart L. |last17=Bosch |first17=Berend-Jan |title=Identification of sialic acid-binding function for the Middle East respiratory syndrome coronavirus spike glycoprotein |journal=Proceedings of the National Academy of Sciences |date=3 October 2017 |volume=114 |issue=40 |pages=E8508–E8517 |doi=10.1073/pnas.1712592114 |pmid=28923942 |pmc=5635925 |bibcode=2017PNAS..114E8508L |s2cid=20912646 |doi-access=free }}</ref>


==History==
==History==
The term ''Lewis'' in its name comes from the name of a family of people who suffered from a red blood cell incompatibility. The studies done on these individuals' red blood cells led to the discovery of sialyl Lewis X. Sialyl Lewis x is a very important red blood cell antigen present on the glycolipids on the plasma membrane of the cell.
The term "Lewis" in the name comes from a family of people with a red blood cell incompatibility. The studies done on these individuals' red blood cells led to the discovery of sialyl-Lewis<sup>X</sup>. Sialyl-Lewis<sup>X</sup> is an important red blood cell antigen present on the glycolipids on the plasma membrane of the cell.


Its localization on the cell surface of cells led to its alternative nomenclature as a [[cluster of differentiation]]. Clusters of differentiation are a naming system devised in 1982 to classify cell-surface antigens on [[leukocytes]] identified via [[monoclonal antibodies]]. Sialyl Lewis X was assigned the name CD15.
Its localization to the cell surface of cells led to its alternative nomenclature as a [[cluster of differentiation]]. Clusters of differentiation are a naming system devised in 1982 to classify cell-surface antigens on [[leukocytes]] identified via [[monoclonal antibodies]]. Sialyl-Lewis<sup>X</sup> was assigned the name CD15.


== See also ==
== See also ==
* [[CA19-9]] (Sialyl-Lewis A)
* [[CA19-9]] (sialyl-Lewis<sup>A</sup>)


==References==
==References==

Latest revision as of 22:55, 14 June 2024

Sialyl-Lewis X
Names
IUPAC name
(5-Acetamido-3,5-dideoxy-D-glycero-α-D-galacto-non-2-ulopyranosylonic acid)-(2→3)-β-D-galactopyranosyl-(1→4)-[α-L-fucopyranosyl-(1→3)]-N-acetyl-D-glucosamine
Systematic IUPAC name
(2S,4S,5R,6R)-5-Acetamido-2-{[(2S,3R,4S,5S,6R)-2-{[(2R,3R,4R,5R)-5-acetamido-1,2-dihydroxy-6-oxo-3-{[(2S,3S,4R,5S,6S)-3,4,5-trihydroxy-6-methyloxan-2-yl]oxy}hexan-3-yl]oxy}-2,4-dihydroxy-6-(hydroxymethyl)oxan-4-yl]oxy}-4-hydroxy-6-[(1R,2R)-1,2,3-trihydroxypropyl]oxane-2-carboxylic acid
Other names
sialyl LeX, SLeX, CD15s, SSEA-1
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
MeSH sialyl+Lewis+X
UNII
  • InChI=1S/C31H52N2O23/c1-9-18(43)21(46)22(47)28(51-9)53-24(12(5-34)32-10(2)38)25(15(42)7-36)54-29-23(48)27(20(45)16(8-37)52-29)56-31(30(49)50)4-13(40)17(33-11(3)39)26(55-31)19(44)14(41)6-35/h5,9,12-29,35-37,40-48H,4,6-8H2,1-3H3,(H,32,38)(H,33,39)(H,49,50)/t9-,12-,13-,14+,15+,16+,17+,18+,19+,20-,21+,22-,23+,24+,25+,26+,27-,28-,29-,31-/m0/s1 checkY
    Key: LAQPKDLYOBZWBT-NYLDSJSYSA-N checkY
  • InChI=1/C31H52N2O23/c1-9-18(43)21(46)22(47)28(51-9)53-24(12(5-34)32-10(2)38)25(15(42)7-36)54-29-23(48)27(20(45)16(8-37)52-29)56-31(30(49)50)4-13(40)17(33-11(3)39)26(55-31)19(44)14(41)6-35/h5,9,12-29,35-37,40-48H,4,6-8H2,1-3H3,(H,32,38)(H,33,39)(H,49,50)/t9-,12-,13-,14+,15+,16+,17+,18+,19+,20-,21+,22-,23+,24+,25+,26+,27-,28-,29-,31-/m0/s1
    Key: LAQPKDLYOBZWBT-NYLDSJSYBC
  • O=C(N[C@@H]1[C@@H](O)C[C@](O[C@H]1[C@H](O)[C@H](O)CO)(O[C@@H]2[C@@H](O)[C@@H](O[C@H](CO)[C@@H]2O)O[C@@H]([C@H](O[C@@H]3O[C@H]([C@@H](O)[C@@H](O)[C@@H]3O)C)[C@H](C=O)NC(=O)C)[C@H](O)CO)C(=O)O)C
Properties
C31H52N2O23
Molar mass 820.744 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Sialyl LewisX (sLeX), also known as cluster of differentiation 15s (CD15s) or stage-specific embryonic antigen 1 (SSEA-1), is a tetrasaccharide carbohydrate which is usually attached to O-glycans on the surface of cells. It is known to play a vital role in cell-to-cell recognition processes. It is also the means by which an egg attracts sperm; first, to stick to it, then bond with it and eventually form a zygote.

Sialyl-LewisX is also one of the most important blood group antigens and is displayed on the terminus of glycolipids that are present on the cell surface. The sialyl-LewisX determinant, E-selectin ligand carbohydrate structure, is constitutively expressed on granulocytes and monocytes and mediates inflammatory extravasation of these cells. Resting T and B lymphocytes lack its expression and are induced to strongly express sialyl-LewisX upon activation. The sialyl-LewisX determinant is expressed preferentially on activated Th1 cells but not on Th2 cells.

Structure

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Sialyl-LewisX is a tetrasaccharide composed of a sialic acid, fucose and an N-acetyllactosamine. Its systematic name is 5-acetylneuraminyl-(2-3)-galactosyl-(1-4)-(fucopyranosyl-(1-3))-N-acetylglucosamine (Neu5Acα2-3Galβ1-4[Fucα1-3]GlcNAcβ). In humans,[1][2] it is synthesized by four fucosyltransferases: FUT3, FUT5, FUT6 and FUT7. The other three enzymes of the sialyltransferase family, ST3GAL3, ST3GAL4, and ST3GAL6, participate in the synthesis of the sialyl-LewisX precursor.[2]

Function

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Leukocyte homing

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Sialyl-LewisX is important in leukocyte tethering and rolling. Leukocytes move through the blood stream and then tether themselves to the endothelial wall and roll along the endothelium before potentially exiting into the tissue. Sialyl-LewisX is a necessary partner for the three selectins that bind the leukocyte and endothelial cells. When sialyl-LewisX is part of an O-glycan and attached to CD34, it can then bind to L-selectin. For the binding to L-selectin to occur, sialyl-LewisX must undergo sulfation. For sialyl-LewisX to bind to P-selectin, an O-linked glycan near the N-terminus of P-selectin glycoprotein ligand-1 (PSGL-1) is modified with sialyl-LewisX and, in combination with nearby tyrosine residues modified with sulfate, forms the binding contact for P-selectin. For sialyl-LewisX to bind to E-selectin, it can be part of either an N-linked or O-linked glycan attached to cell surface glycoproteins such as PSGL-1, CD43 or CD44. This sialyl-LewisX-mediated binding to selectins allows circulating leukocytes to stick to and roll along endothelial cells lining blood vessels, thereby enabling the leukocytes to accumulate at a site of vascular inflammation.

Fertilization

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Sialyl-LewisX allows a sperm cell to recognize and fertilize an egg cell. For fertilization to occur, human sperm must bind to the zona pellucida (ZP), the translucent matrix covering the human egg composed of four glycoproteins—ZP1, 2, 3, and 4—and transit through the matrix in order to fuse with the oocyte.[3] The human ZP is coated with dense N- and O-glycans that are terminated with the sialyl-LewisX sequence.[4] The hemizona assay, which assesses sperm–ZP binding by counting the number of sperm bound to hemispheres of bisected nonliving human eggs in vitro, reveals that 0.5 mM sialyl-LewisX inhibits sperm–ZP binding by 63%.[4] Furthermore, adding purified and solubilized ZP3 or ZP4 from the human oocyte dose-dependently inhibits sperm–ZP binding in the hemizona assay.[5] Such evidence suggest that the early steps of human sperm–egg binding may be mediated by lectins for sialyl-LewisX present on human sperm.

Clinical significance

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Leukocyte adhesion deficiency

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Main article: Congenital disorder of glycosylation type IIc

Defective synthesis of the sialyl-LewisX antigen results in immunodeficiency (leukocyte adhesion deficiency type 2). Defective synthesis can be caused by the loss of fucosyltransferase, impairing the glycosylation of the glycosphingolipid. Sialyl-LewisX is being researched for detection and treatment of immune disorders because of its presence on leukocytes.

Blood cancers

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Sialyl-LewisX mediates phagocytosis and chemotaxis, found in neutrophils;[6] it is expressed by cells present in Hodgkin disease, some B-cell chronic lymphocytic leukemias, acute lymphoblastic leukemias, and most acute nonlymphocytic leukemias. CD15 is present on almost all Reed–Sternberg cells, including their rare mononuclear variants, and, as such, can be used in immunohistochemistry to identify the presence of such cells in biopsies. The presence of these cells is diagnostic of Hodgkin's lymphoma. Reed–Sternberg cells display a characteristic pattern of sialyl-LewisX positivity, with membranous staining combined with staining of the Golgi apparatus. Immunohistochemical panels for the diagnosis of Hodgkin's disease typically employ CD15 along with CD30 and CD45; the latter does not stain Reed–Sternberg cells, but does stain almost all other lymphoid cells. Sialyl-LewisX is also present in about 50% of adenocarcinoma cells and can be used to distinguish such conditions from mesothelioma, which is typically negative.[7]

Cancer metastasis

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Sialyl-LewisX plays a critical role in cancer metastasis, facilitating the extravasation of cancer cells out of the bloodstream when they are moving through the body. Its expression is related to tumor stage, recurrence, and overall patient survival.[8] Therefore, sialyl Lewis x is being used as a target in studies to fight tumors and cancer cell growth. There is frequent overexpression of sialyl-LewisX on cancer cells, and it is found on both N-glycan and O-glycans. Sialyl-LewisX is being researched with CD markers to find new ways to create biosensors for cancer cells. It is also being used in new ways to target cancer cells specifically for cancer treatment.

In vitro fertilization

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Further information: In vitro fertilization

Sialyl-LewisX is being used to achieve greater rates of fertilization of eggs in women by coating the eggs with sialyl-LewisX.

Immunity and inflammation

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Sialyl-LewisX plays a key role in the inflammatory response and may be used to increase the leukocyte response to infections. Sialyl-LewisX is also an inflammation-associated antigen on liver cells. It is overexpressed on diseased liver cells and can be used as a way to detect liver disease in a patient.

MERS coronavirus binding

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In June 2019, before the onset of the COVID-19 pandemic, the receptor for sulfated sialyl-LewisX oligosaccharide (particularly with α2,3 linkages) was found to be the preferred binding site, both in humans and in dromedary camels, for the coronavirus causing Middle East respiratory syndrome (MERS), the sixth coronavirus to be described.[9][10]

History

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The term "Lewis" in the name comes from a family of people with a red blood cell incompatibility. The studies done on these individuals' red blood cells led to the discovery of sialyl-LewisX. Sialyl-LewisX is an important red blood cell antigen present on the glycolipids on the plasma membrane of the cell.

Its localization to the cell surface of cells led to its alternative nomenclature as a cluster of differentiation. Clusters of differentiation are a naming system devised in 1982 to classify cell-surface antigens on leukocytes identified via monoclonal antibodies. Sialyl-LewisX was assigned the name CD15.

See also

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References

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  1. ^ de Vries, T.; Knegtel, R. M.; Holmes, E. H.; Macher, B. A. (October 2001). "Fucosyltransferases: structure/function studies". Glycobiology. 11 (10): 119R–128R. doi:10.1093/glycob/11.10.119r. ISSN 0959-6658. PMID 11588153.
  2. ^ a b Trinchera, Marco; Aronica, Adele; Dall’Olio, Fabio (2017-02-23). "Selectin Ligands Sialyl-Lewis a and Sialyl-Lewis x in Gastrointestinal Cancers". Biology. 6 (1): 16. doi:10.3390/biology6010016. ISSN 2079-7737. PMC 5372009. PMID 28241499.
  3. ^ Clark, G. F. (2013). "The role of carbohydrate recognition during human sperm-egg binding". Human Reproduction. 28 (3): 566–577. doi:10.1093/humrep/des447. PMID 23315069.
  4. ^ a b Pang, Poh-Choo; Chiu, Philip C. N.; et al. (18 August 2011). "Human Sperm Binding Is Mediated by the Sialyl-Lewisx Oligosaccharide on the Zona Pellucida". Science. 333 (6050): 1761–1764. Bibcode:2011Sci...333.1761P. doi:10.1126/science.1207438. hdl:10044/1/15584. PMID 21852454. S2CID 23610213.
  5. ^ Chiu, P. C. N.; Wong, B. S. T.; Chung, M. -K.; Lam, K. K. W.; Pang, R. T. K.; Lee, K. -F.; Sumitro, S. B.; Gupta, S. K.; Yeung, W. S. B. (2008). "Effects of Native Human Zona Pellucida Glycoproteins 3 and 4 on Acrosome Reaction and Zona Pellucida Binding of Human Spermatozoa". Biology of Reproduction. 79 (5): 869–877. doi:10.1095/biolreprod.108.069344. PMID 18667750.
  6. ^ Kerr MA, Stocks SC (November 1992). "The role of CD15-(Le(X))-related carbohydrates in neutrophil adhesion". Histochem. J. 24 (11): 811–26. doi:10.1007/BF01046353. PMID 1362195. S2CID 8602651.
  7. ^ Leong, Anthony S-Y; Cooper, Kumarason; Leong, F Joel W-M (2003). Manual of Diagnostic Cytology (2nd ed.). Greenwich Medical Media, Ltd. pp. 83–84. ISBN 1-84110-100-1.
  8. ^ Liang, Jin-xiao; Liang, Yong; Gao, Wei (2016-05-24). "Clinicopathological and prognostic significance of sialyl Lewis X overexpression in patients with cancer: a meta-analysis". OncoTargets and Therapy. 9: 3113–3125. doi:10.2147/OTT.S102389. ISSN 1178-6930. PMC 4888715. PMID 27307752.
  9. ^ Tortorici, M. Alejandra; Walls, Alexandra C.; Lang, Yifei; Wang, Chunyan; Li, Zeshi; Koerhuis, Danielle; Boons, Geert-Jan; Bosch, Berend-Jan; Rey, Félix A.; de Groot, Raoul J.; Veesler, David (June 2019). "Structural basis for human coronavirus attachment to sialic acid receptors". Nature Structural & Molecular Biology. 26 (6): 481–489. doi:10.1038/s41594-019-0233-y. PMC 6554059. PMID 31160783.
  10. ^ Li, Wentao; Hulswit, Ruben J. G.; Widjaja, Ivy; Raj, V. Stalin; McBride, Ryan; Peng, Wenjie; Widagdo, W.; Tortorici, M. Alejandra; Dieren, Brenda van; Lang, Yifei; Lent, Jan W. M. van; Paulson, James C.; Haan, Cornelis A. M. de; Groot, Raoul J. de; Kuppeveld, Frank J. M. van; Haagmans, Bart L.; Bosch, Berend-Jan (3 October 2017). "Identification of sialic acid-binding function for the Middle East respiratory syndrome coronavirus spike glycoprotein". Proceedings of the National Academy of Sciences. 114 (40): E8508–E8517. Bibcode:2017PNAS..114E8508L. doi:10.1073/pnas.1712592114. PMC 5635925. PMID 28923942. S2CID 20912646.

Further reading

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