Abstract
Heme carrier HasA has a unique type of histidine/tyrosine heme iron ligation in which the iron ion is in a thermally driven two spin states equilibrium. We recently suggested that the H-bonding between Tyr75 and the invariantly conserved residue His83 modulates the strength of the iron-Tyr75 bond. To unravel the role of His83, we characterize the iron ligation and the electronic properties of both wild type and H83A mutant by a variety of spectroscopic techniques. Although His83 in wild type modulates the strength of the Tyr-iron bond, its removal causes detachment of the tyrosine ligand, thus giving rise to a series of pH-dependent equilibria among species with different axial ligation. The five coordinated species detected at physiological pH may represent a possible intermediate of the heme transfer mechanism to the receptor.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Bacterial Proteins / chemistry*
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Bacterial Proteins / genetics
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Bacterial Proteins / metabolism
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Carrier Proteins / chemistry*
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Carrier Proteins / genetics
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Carrier Proteins / metabolism
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Heme / chemistry*
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Heme / genetics
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Heme / metabolism
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Histidine / chemistry*
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Histidine / genetics
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Histidine / metabolism
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Hydrogen-Ion Concentration
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Iron / chemistry*
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Iron / metabolism
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Membrane Proteins / chemistry*
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Mutation, Missense
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Protein Binding
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Protein Structure, Tertiary
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Serratia marcescens / chemistry*
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Serratia marcescens / genetics
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Serratia marcescens / metabolism
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Structure-Activity Relationship
Substances
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Bacterial Proteins
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Carrier Proteins
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HasA protein, Serratia marcescens
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Membrane Proteins
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Heme
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Histidine
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Iron