STRUCTURAL CHARACTERIZATION OF THE XANTHOMONAS CITRI’s T4SS PERIPLASMIC DOMAINS

Bacteria use secretion systems to translocate macromolecules across the cellular envelope. These very large macromolecular complexes mediate a diverse range of functions, including DNA conjugation and the secretion of virulence factors. The Type IV Secretion System of the phytopathogen Xanthomonas citri (T4SS_XAC) is involved in the secretion of toxins that kill other gram-negative bacteria. While a recent Cryo-EM model of the conjugative T4SS provided crucial information regarding the architecture of this system, structural details about key periplasmic regions, such as the TrwE (VirB10) N-terminal domain, are still missing, and the structural details of TrwG (VirB8) periplasmic domains had very low resolution. Furthermore, the effectors translocator T4SS_XAC was not extensively characterized. In fact, only the T4SS_XAC core complex was structurally characterized to date. In addition, the VirB8_XAC differs from TrwG because it has a much larger and potentially disordered C-terminal tail. Therefore, to gain further information on the organization of T4SS_XAC periplasmic region we designed four VirB8 constructs with and without the disordered C-terminal tail. We expressed and purified three of them, and we will investigate their oligomerization properties and the potential interaction with VirB10. 

This work was supported by the São Paulo Research Foundation (FAPESP 2021/10577-0 and 2017/17303-7).