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. 2010 Feb;303(1):76-83.
doi: 10.1111/j.1574-6968.2009.01863.x. Epub 2009 Nov 23.

A weak DD-carboxypeptidase activity explains the inability of PBP 6 to substitute for PBP 5 in maintaining normal cell shape in Escherichia coli

Chiranjit Chowdhury  1 , Tapas R Nayak, Kevin D Young, Anindya S Ghosh
Affiliations

A weak DD-carboxypeptidase activity explains the inability of PBP 6 to substitute for PBP 5 in maintaining normal cell shape in Escherichia coli

Chiranjit Chowdhury et al. FEMS Microbiol Lett. 2010 Feb.

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.

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Figures

Fig. 1
Fig. 1. Location of the “morphology maintenance domain” (MMD) of PBP 5
Top view: Arrows point to residues of sPBP 5 important for catalysis.
Fig. 2
Fig. 2. SDS-PAGE analysis of purified sPBPs and their mosaics
Purified sPBPs (3 μg) were stained with Coomassie blue (A), or with BOCILLIN FL (B). Lane M, Protein molecular weight markers; Lane 1, sPBP 5; Lane 2, sPBP 6; Lane 3, sPBP 656; and Lane 4, sPBP 565.
See this image and copyright information in PMC

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