Abstract
The bacterial cell wall is a polymer consisting of alternating N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) units, cross-linked via peptides appended to MurNAc. The final steps in the formation of cell wall, also referred to as murein, are catalyzed by high-molecular-weight, class A penicillin-binding proteins (PBPs). These bifunctional enzymes catalyze both glycosyltransfer, to form the carbohydrate backbone of murein, and transpeptidation, to form the interstrand peptide linkages. Using PBP1b from Eschericia coli, an in vitro kinetic characterization of the glycosyltransfer reaction was carried out. Initial studies with unlabeled substrate (Lipid II) revealed that activity is strongly influenced by DMSO, as well as metal and detergent. In addition, a continuous fluoresence assay was developed and used to determine the effect of pH on the reaction. A single basic residue was titrated, with a pK(a) of 7.0. Taken together, these data suggest a mechanism for PBP1b where the glycosyltransfer reaction is catalyzed by the concerted effect of an active site base to deprotonate the glycosyl acceptor and a divalent metal to assist departure of the leaving group of the glycosyl donor.
MeSH terms
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Bacterial Proteins*
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Carrier Proteins / analysis
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Carrier Proteins / chemistry*
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Chromatography, High Pressure Liquid
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Dansyl Compounds / chemistry
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Enzyme Activation
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Escherichia coli Proteins / analysis
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Escherichia coli Proteins / chemistry*
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Fluorometry / methods
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Glycosyltransferases / analysis
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Glycosyltransferases / chemistry*
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Hexosyltransferases*
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Kinetics
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Multienzyme Complexes / analysis
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Multienzyme Complexes / chemistry
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Muramoylpentapeptide Carboxypeptidase / analysis
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Muramoylpentapeptide Carboxypeptidase / chemistry*
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Nuclear Magnetic Resonance, Biomolecular
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Penicillin-Binding Proteins
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Peptidoglycan Glycosyltransferase*
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Peptidyl Transferases / analysis
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Peptidyl Transferases / chemistry*
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Recombinant Proteins / analysis
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Recombinant Proteins / chemistry
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Serine-Type D-Ala-D-Ala Carboxypeptidase*
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Substrate Specificity
Substances
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Bacterial Proteins
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Carrier Proteins
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Dansyl Compounds
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Escherichia coli Proteins
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Multienzyme Complexes
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Penicillin-Binding Proteins
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Recombinant Proteins
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Peptidyl Transferases
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Glycosyltransferases
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Hexosyltransferases
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Peptidoglycan Glycosyltransferase
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penicillin-binding protein 1B, E coli
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murein transglycosylase
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Serine-Type D-Ala-D-Ala Carboxypeptidase
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Muramoylpentapeptide Carboxypeptidase