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Neisseria gonorrhoeae Penicillin-Binding Protein 3 Demonstrates a Pronounced Preference for Nε-Acylated Substrates

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journal contribution
posted on 23.06.2009, 00:00 by Sridhar Peddi, Robert A. Nicholas, William G. Gutheil
Penicillin-binding proteins (PBPs) are bacterial enzymes involved in the final stages of cell wall biosynthesis and are the lethal targets of β-lactam antibiotics. Despite their importance, their roles in cell wall biosynthesis remain enigmatic. A series of eight substrates, based on variation of the pentapeptide Boc-l-Ala-γ-d-Glu-l-Lys-d-Ala-d-Ala, were synthesized to test specificity for three features of PBP substrates: (1) the presence or absence of an Nε-acyl group, (2) the presence of d-IsoGln in place of γ-d-Glu, and (3) the presence or absence of the N-terminal l-Ala residue. The capacity of these peptides to serve as substrates for Neisseria gonorrhoeae (NG) PBP3 was assessed. NG PBP3 demonstrated good catalytic efficiency (2.5 × 105 M−1 s−1) with the best of these substrates, with a pronounced preference (50-fold) for Nε-acylated substrates over Nε-nonacylated substrates. This observation suggests that NG PBP3 is specific for the ∼d-Ala-d-Ala moiety of pentapeptides engaged in cross-links in the bacterial cell wall, such that NG PBP3 would act after transpeptidase-catalyzed reactions generate the acylated amino group required for its specificity. NG PBP3 demonstrated low selectivity for γ-d-Glu vs d-IsoGln and for the presence or absence of the terminal l-Ala residue. The implications of this substrate specificity of NG PBP3 with respect to its possible role in cell wall biosynthesis, and for understanding the substrate specificity of the LMM PBPs in general, are discussed.