VirB7 and VirB9 Interactions Are Required for the Assembly and Antibacterial Activity of a Type IV Secretion System

• Published in: Structure (London) 2016-10, Vol.24 (10), p.1707-1718
• Main Authors: Oliveira, Luciana Coutinho, Souza, Diorge Paulo, Oka, Gabriel Umaji, Lima, Filipe da Silva, Oliveira, Ronaldo Junio, Favaro, Denize Cristina, Wienk, Hans, Boelens, Rolf, Farah, Chuck Shaker, Salinas, Roberto Kopke
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Models, Molecular; Protein Binding; Protein Stability; Protein Structure, Secondary; Type IV Secretion Systems - chemistry; Type IV Secretion Systems - metabolism; Xanthomonas - metabolism
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2016.07.015

The type IV secretion system (T4SS) from the phytopathogen Xanthomonas citri (Xac) is a bactericidal nanomachine. The T4SS core complex is a ring composed of multiple copies of VirB7-VirB9-VirB10 subunits. Xac-VirB7 contains a disordered N-terminal tail (VirB7NT) that recognizes VirB9, and a C-terminal domain (VirB7CT) involved in VirB7 self-association. Here, we show that VirB7NT forms a short β strand upon binding to VirB9 and stabilizes it. A tight interaction between them is essential for T4SS assembly and antibacterial activity. Abolishing VirB7 self-association or deletion of the VirB7 C-terminal domain impairs this antibacterial activity without disturbing T4SS assembly. These findings reveal protein interactions within the core complex that are critical for the stability and activity of a T4SS. [Display omitted] •Binding to VirB7NT stabilizes VirB9CT•The structural basis of the recognition between VirB7 and VirB9 is revealed•Disruption of VirB7-VirB9 interaction affects T4SS assembly and killing activity•Interactions between VirB7 subunits are essential for a functional T4SS Oliveira et al. show that tight binding of VirB7 to VirB9 is essential for assembly of the antibacterial type IV secretion system (T4SS) in the citrus pathogen Xanthomonas citri, whereas removal of the non-canonical VirB7 C-terminal domain, or impairment of VirB7 self-association, does not perturb assembly but abolishes T4SS activity.