Open AccessInteractions between Brucella suis VirB8 and Its Homolog TraJ from the Plasmid pSB102 Underline the Dynamic Nature of Type IV Secretion Systems
Author(s) -
Gisèle Bourg,
Romain Sube,
David O’Callaghan,
Gilles Patey
Publication year - 2009
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.01426-08
Subject(s) - periplasmic space , biology , secretion , mutant , transmembrane domain , type vi secretion system , agrobacterium tumefaciens , wild type , plasmid , cytoplasm , microbiology and biotechnology , gene , virulence , genetics , escherichia coli , transformation (genetics) , biochemistry
The proteinVirB8 plays a critical role in the assembly and function of theAgrobacterium tumefaciens virB type IV secretion system (T4SS). The structure of the periplasmic domain of bothA .tumefaciens andBrucella suis VirB8 has been determined, and site-directed mutagenesis has revealed amino acids involved in the dimerization of VirB8 and interactions with VirB4 and VirB10. We have shown previously that TraJ, the VirB8 homologue from pSB102, and the chimeric protein TraJB8, encompassing the cytoplasmic and transmembrane (TM) domains of TraJ and the periplasmic domain of VirB8, were unable to complement aB .suis mutant containing an in-frame deletion of thevirB8 gene. This suggested that the presence of the TraJ cytoplasmic and TM domains could block VirB8 dimerization or assembly in the inner membrane. By bacterial two-hybrid analysis, we found that VirB8, TraJ, and the chimeras can all interact to form both homo- and heterodimers. However, the presence of the TM domain of TraJ resulted in much stronger interactions in both the homo- and heterodimers. We expressed the wild-type and chimeric proteins in wild-typeB .suis . The presence of proteins carrying the TM domain of TraJ had a dominant negative effect, leading to complete loss of virulence. This suggests that the T4SS is a dynamic structure and that strong interactions block the spatial flexibility required for correct assembly and function.