Peptidoglycan binding by a pocket on the accessory NTF2-domain of Pgp2 directs the helical cell shape of Campylobacter jejuni

Abstract

Every year, over 600 million people worldwide contract campylobacteriosis, a bacterial food-borne gastroenteritis primarily caused by Campylobacter jejuni. The helical cell shape of C. jejuni, a key colonization factor, is determined by the structure of the peptidoglycan (PG) layer. The helical structure of PG is determined by Pgp2, a LD-carboxypeptidase that cleaves the terminal D-Ala residue from both monomeric and cross-linked PG tetrapeptides. The interaction interface between Pgp2 and PG to select sites for peptide trimming is unknown. Here, we report a 1.6 Å resolution crystal structure that contains a conserved LD-carboxypeptidase domain and a previously uncharacterized domain with an NTF2-like fold (NTF2). We identified a pocket in the NTF2 domain formed by conserved residues that is located approximately 40 Å from the LD-carboxypeptidase active site. Sitedirected mutagenesis combined with NMR-monitored titration studies were used to define the interaction interfaces of Pgp2 with several PG fragments, which bound to the active site within the LD-carboxypeptidase domain and the pocket of the NTF2 domain. We propose a model for Pgp2 binding to PG strands involving both the LDcarboxypeptidase and the NTF2 domains to guide catalytic activity to induce a helical cell shape.

Asymmetric peptidoglycan editing generates cell curvature in Bdellovibrio predatory bacteria

“…5d). This helix was the major NTF2 feature that was reported to shift upon Pgp2-PG binding 50 . We postulate that its position has been modified in our Bd1075 structure by sidechains contacting the P107/K108 loop and may thus represent a 'bound' state.…”

“…The NTF2 domain of C. jejuni Pgp2 was recently found by NMR studies to bind a variety of PG fragments, with specific secondary structure features shifting upon complexation 50 . The general agreement of some of the structures of monomeric Bd1075 with dimeric Pgp2 is suggestive that Bd1075 binds PG.…”

“…We postulate that its position has been modified in our Bd1075 structure by sidechains contacting the P107/K108 loop and may thus represent a 'bound' state. There is also the potential for NTF2:LD-CPase domain crosstalk, given that a small LD-CPase domain helix (aa 125-132) shifts in response to NTF2 alterations 50 , and in Bd1075 appears to influence the disorder of the adjacent active site lid domain.…”