Ankyrin-mediated self-protection during cell invasion by the bacterial predator Bdellovibrio bacteriovorus.

Carey Lambert,Rob Till,R Elizabeth Sockett,Ian T Cadby,Waldemar Vollmer,Andrew L Lovering,Thomas R Lerner,David J Lee,William S Hughes,Luke J Alderwick,Nhat Khai Bui

doi:10.1038/ncomms9884

Abstract

Predatory Bdellovibrio bacteriovorus are natural antimicrobial organisms, killing other bacteria by whole-cell invasion. Self-protection against prey-metabolizing enzymes is important for the evolution of predation. Initial prey entry involves the predator's peptidoglycan DD-endopeptidases, which decrosslink cell walls and prevent wasteful entry by a second predator. Here we identify and characterize a self-protection protein from B. bacteriovorus, Bd3460, which displays an ankyrin-based fold common to intracellular pathogens of eukaryotes. Co-crystal structures reveal Bd3460 complexation of dual targets, binding a conserved epitope of each of the Bd3459 and Bd0816 endopeptidases. Complexation inhibits endopeptidase activity and cell wall decrosslinking in vitro. Self-protection is vital — ΔBd3460 Bdellovibrio deleteriously decrosslink self-peptidoglycan upon invasion, adopt a round morphology, and lose predatory capacity and cellular integrity. Our analysis provides the first mechanistic examination of self-protection in Bdellovibrio, documents protection-multiplicity for products of two different genomic loci, and reveals an important evolutionary adaptation to an invasive predatory bacterial lifestyle.

Highlights

Predatory Bdellovibrio bacteriovorus are natural antimicrobial organisms, killing other bacteria by whole-cell invasion
We demonstrate that endopeptidase complexation by Bd3460 prevents cell wall decrosslinking, and that both the Bd0816 and Bd3459 targets bind this self-protection protein via a common epitope
Ankyrin-repeat proteins (ARPs) are rare in bacteria, but are enriched in intracellular parasites of eukaryotes where they are used to modulate host cell processes[11]

Summary

Introduction

Predatory Bdellovibrio bacteriovorus are natural antimicrobial organisms, killing other bacteria by whole-cell invasion. This rounding is caused by prey peptidoglycan cell wall modification, catalysed by Bdellovibrio enzymes[6]. We assigned prey cell rounding to the action of two secreted Bdellovibrio peptidoglycan DD-endopeptidases, Bd0816 and Bd3459, that act to modify the invaded cell wall via hydrolysis of the structural 3-4 peptide crosslinks[6].

Results

Conclusion