Monomer‐to‐dimer transition of Brucella suis type IV secretion system component VirB8 induces conformational changes. (23rd March 2017) - Sharifahmadian, Mahzad
Abstract : Secretion systems are protein complexes essential for bacterial virulence and potential targets for antivirulence drugs. In the intracellular pathogen Brucella suis, a type IV secretion system mediates the translocation of virulence factors into host cells and it is essential for pathogenicity. VirB8 is a core component of the secretion system and dimerization is important for functionality of the protein complex. We set out to study dimerization and possible conformational changes of VirB8 from B. suis (VirB8s) using nuclear magnetic resonance, X‐ray crystallography, and differential scanning fluorimetry. We identified changes of the protein induced by a concentration‐dependent monomer‐to‐dimer transition of the periplasmic domain (VirB8sp). We also show that the presence of the detergent CHAPS alters several signals in the heteronuclear single quantum coherence (HSQC) spectra and some of these chemical shift changes correspond to those observed during monomer–dimer transition. X‐ray analysis of a monomeric variant (VirB8sp M102R ) demonstrates that significant structural changes occur in the protein's α‐helical regions (α2 and α4). We localized chemical shift changes of residues at the dimer interface as well as to the α1 helix that links this interface to a surface groove that binds dimerization inhibitors. Fragment‐based screening identified small molecules that bind to VirB8sp and two of them have differential binding affinity for wild‐type and the VirB8sp M102R variant underlining their different conformations. The observed chemical shift changes suggest conformational changes of VirB8s during monomer–dimer transition that may play a role during secretion system assembly or function and they provide insights into the mechanism of inhibitor action. Database: BMRB accession no. 26852 and PDB5JBS . Abstract : Considering the rise of antibiotic resistance, studying the inhibition of bacterial virulence factors is a pertinent strategy that may lead to better treatments for infectious diseases. VirB8 is an essential component of bacterial type IV secretion systems that contribute to the virulence of many pathogens. Here, we describe the structural dynamics of VirB8 and strategies for inhibitor design.