Anchoring the T6SS to the cell wall: Crystal structure of the peptidoglycan binding domain of the TagL accessory protein.

Van Son Nguyen,Éric Cascales,Christian Cambillau,Alain Roussel,Silvia Spinelli,Philippe Leone,Erh-Min Lai

doi:10.1371/journal.pone.0254232

Abstract

The type VI secretion system (T6SS) is a widespread mechanism of protein delivery into target cells, present in more than a quarter of all sequenced Gram-negative bacteria. The T6SS constitutes an important virulence factor, as it is responsible for targeting effectors in both prokaryotic and eukaryotic cells. The T6SS comprises a tail structure tethered to the cell envelope via a trans-envelope complex. In most T6SS, the membrane complex is anchored to the cell wall by the TagL accessory protein. In this study, we report the first crystal structure of a peptidoglycan-binding domain of TagL. The fold is conserved with members of the OmpA/Pal/MotB family, and more importantly, the peptidoglycan binding site is conserved. This structure further exemplifies how proteins involved in anchoring to the cell wall for different cellular functions rely on an interaction network with peptidoglycan strictly conserved.

Highlights

During evolution, Gram-negative bacteria have evolved sophisticated mechanisms to hunt their prey or run away from their predators
A previous study has shown that the entero-aggregative Escherichia coli (EAEC) TagL subunit bears a peptidoglycan-binding domain (PGBD) that is required for the function of the Sci-1 T6SS
HHpred returned a long list of homologous structures with HHpred probability > 99.9%. They all belong to the outer membrane protein A (OmpA) family or OmpA-like domains

Summary

Introduction

Gram-negative bacteria have evolved sophisticated mechanisms to hunt their prey or run away from their predators. The type VI secretion system is a widespread mechanism found in more than a quarter of all sequenced Gram-negative bacteria, with one or several copies in each species [3,4,5]. This nanomachine transports protein effectors directly from the cytoplasm across the cell envelope and injects them into the target cells, both prokaryotic and eukaryotic [6,7,8,9].

Methods

Results

Conclusion