title: A weak DD-carboxypeptidase activity explains the inability of PBP 6 to substitute for PBP 5 in maintaining normal cell shape in Escherichia coli.
abstract: Penicillin-binding protein (PBP) 5 plays a critical role in maintaining normal cellular morphology in mutants of Escherichia coli lacking multiple PBPs. The most closely related homologue, PBP 6, is 65% identical to PBP 5, but is unable to substitute for PBP 5 in returning these mutants to their wild-type shape. The relevant differences between PBPs 5 and 6 are localized in a 20-amino acid stretch of domain I in these proteins, which includes the canonical KTG motif at the active site. We determined how these differences affected the enzymatic properties of PBPs 5 and 6 toward beta-lactam binding and the binding and hydrolysis of two peptide substrates. We also investigated the enzymatic properties of recombinant fusion proteins in which active site segments were swapped between PBPs 5 and 6. The results suggest that the in vivo physiological role of PBP 5 is distinguished from PBP 6 by the higher degree of DD-carboxypeptidase activity of the former.
authors.affiliation: Department of Biotechnology, Indian Institute of Technology, Kharagpur, West Bengal, India.
authors.forename: Chiranjit
authors.initials: C
authors.lastname: Chowdhury
authors.forename: Tapas R
authors.initials: TR
authors.lastname: Nayak
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Young
authors.forename: Anindya S
authors.initials: AS
authors.lastname: Ghosh
mesh_terms: D020816:Amino Acid Motifs; D000900:Anti-Bacterial Agents / Q000378:metabolism; D002268:Carboxypeptidases / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D002473:Cell Wall / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology* / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D005816:Genetic Complementation Test; D006868:Hydrolysis; D008958:Models, Molecular; D046915:Penicillin-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D046915:Penicillin-Binding Proteins; D047090:beta-Lactams; D002268:Carboxypeptidases