Miglena E. Stefanova , Christopher Davies , Robert A. Nicholas , William G. Gutheil
{"title":"pH, inhibitor, and substrate specificity studies on Escherichia coli penicillin-binding protein 5","authors":"Miglena E. Stefanova , Christopher Davies , Robert A. Nicholas , William G. Gutheil","doi":"10.1016/S0167-4838(02)00311-4","DOIUrl":null,"url":null,"abstract":"<div><p>The recent structural determination of <em>Escherichia coli</em> penicillin-binding protein 5 (PBP 5) provides the opportunity for detailed structure–function studies of this enzyme. PBP 5 was investigated in terms of its stability, linear reaction kinetics, acyl-donor substrate specificity, inhibition by a number of active site-directed reagents, and pH profile. PBP 5 demonstrated linear reaction kinetics for up to several hours. Dilution of PBP 5 generally resulted in substantial loss of activity, unless BSA or a BSA derivative was added to the diluting buffer. PBP 5 did not demonstrate a significant preference against a simple set of five α- and ε-substituted <span>l</span>-Lys-<span>d</span>-Ala-<span>d</span>-Ala derivatives, suggesting that PBP 5 lacks specificity for the cross-linked state of cell wall substrates. Among a number of active site-directed reagents, only some thiol-directed reagents gave substantial inhibition. Notably, serine-directed reagents, organic phosphates, and simple boronic acids were ineffective as inhibitors. PBP 5 was stable over the pH range 4.6–12.3, and the <em>k</em><sub>cat</sub>/<em>K</em><sub>m</sub> vs. pH profile for activity against Ac<sub>2</sub>-<span>l</span>-Lys-<span>d</span>-Ala-<span>d</span>-Ala was bell-shaped, with p<em>K</em><sub>a</sub>s at 8.2 and 11.1. This is the first complete pH profile, including both acidic and basic limbs, for a PBP-catalyzed <span>dd</span>-carboxypeptidase (CPase) reaction. Based on its structure, similarity to Class A β-lactamases, and results from mutagenesis studies, the acidic and basic limbs of the pH profile of PBP 5 are assigned to Lys-47 and Lys-213, respectively. This assignment supports a role for Lys-47 as the general base for acylation and deacylation reactions.</p></div>","PeriodicalId":100166,"journal":{"name":"Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2002-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0167-4838(02)00311-4","citationCount":"38","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0167483802003114","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 38
Abstract
The recent structural determination of Escherichia coli penicillin-binding protein 5 (PBP 5) provides the opportunity for detailed structure–function studies of this enzyme. PBP 5 was investigated in terms of its stability, linear reaction kinetics, acyl-donor substrate specificity, inhibition by a number of active site-directed reagents, and pH profile. PBP 5 demonstrated linear reaction kinetics for up to several hours. Dilution of PBP 5 generally resulted in substantial loss of activity, unless BSA or a BSA derivative was added to the diluting buffer. PBP 5 did not demonstrate a significant preference against a simple set of five α- and ε-substituted l-Lys-d-Ala-d-Ala derivatives, suggesting that PBP 5 lacks specificity for the cross-linked state of cell wall substrates. Among a number of active site-directed reagents, only some thiol-directed reagents gave substantial inhibition. Notably, serine-directed reagents, organic phosphates, and simple boronic acids were ineffective as inhibitors. PBP 5 was stable over the pH range 4.6–12.3, and the kcat/Km vs. pH profile for activity against Ac2-l-Lys-d-Ala-d-Ala was bell-shaped, with pKas at 8.2 and 11.1. This is the first complete pH profile, including both acidic and basic limbs, for a PBP-catalyzed dd-carboxypeptidase (CPase) reaction. Based on its structure, similarity to Class A β-lactamases, and results from mutagenesis studies, the acidic and basic limbs of the pH profile of PBP 5 are assigned to Lys-47 and Lys-213, respectively. This assignment supports a role for Lys-47 as the general base for acylation and deacylation reactions.