Structural Insights into the Lipoprotein Outer Membrane Regulator of Penicillin-binding Protein 1B

Dustin T King,Emilie Lameignere,Natalie C.J Strynadka

doi:10.1074/jbc.m114.565879

Dustin T King, Emilie Lameignere + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m114.565879

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Abstract

In bacteria, the synthesis of the protective peptidoglycan sacculus is a dynamic process that is tightly regulated at multiple levels. Recently, the lipoprotein co-factor LpoB has been found essential for the in vivo function of the major peptidoglycan synthase PBP1b in Enterobacteriaceae. Here, we reveal the crystal structures of Salmonella enterica and Escherichia coli LpoB. The LpoB protein can be modeled as a ball and tether, consisting of a disordered N-terminal region followed by a compact globular C-terminal domain. Taken together, our structural data allow us to propose new insights into LpoB-mediated regulation of peptidoglycan synthesis.

Highlights

LpoB regulates the activity of the bifunctional peptidoglycan synthase (PBP1b), located in the inner membrane in Enterobacteriaceae
There are likely several cellular factors that affect LpoBPBP1b complex formation and peptidoglycan synthesis. Both binding partners are anchored to distinct biological membranes and have restricted diffusion, a factor that has been proposed in other systems to directly modulate complex formation [47]
Additional interactions by PBP1b, both to self in the observed dimeric oligomerization state of the enzyme as well as to a number of proposed cellular partners, including the cell-division-specific lipoprotein FtsN, the septal transpeptidase PBP3, and the lytic transglycosylase MipA (48 – 50), are important factors to consider in potential modulation of LpoB-PBP1b complex formation

Summary

Background

LpoB regulates the activity of the bifunctional peptidoglycan synthase (PBP1b), located in the inner membrane in Enterobacteriaceae. The rapid emergence of bacterial resistance mechanisms to these agents demands that we better understand additional regulatory factors required for PG synthesis to identify novel drug targets. The final stages of PG synthesis involve attaching new lipid II precursor molecules onto the pre-existing sacculus To accomplish this task, two enzymatic activities are required: (i) glycosyltransferases (GTases) covalently link the GlcNac-MurNac pentapeptide unit from lipid II onto the GlcNac-MurNac backbone of a nascent PG chain, and (ii) transpeptidases (TPases) cross-link newly incorporated donor pentapeptides to pre-existing acceptor peptides in the PG layer [3]. A recent report has indicated that both PBP1b and LpoB are required for PG recovery following lysozyme-induced spheroplast formation in E. coli [11] These reports provide the first evidence that PG synthesis is in part regulated by the bacterial outer membrane in a species-specific manner. The structures allow us to propose a revised model for LpoB-mediated regulation of PBP1b activity

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

CONCLUSION