Edited by Stuart Ferguson Keywords:Bacterial two hybrid Type 4 secretion system VirB8 VirB10 Brucella a b s t r a c t VirB8 is a critical component of the Brucella suis type IV secretion system (T4SS). We previously showed that the transmembrane (TM) domain plays an essential role in interactions of this protein with itself and the other proteins of the T4SS. We report that a point mutation in this TM domain stabilizes homodimers of VirB8 and heterodimers with VirB10. A similar variant of Agrobacterium tumefaciens VirB8 showed the same phenotype. The B. suis VirB8 variant was unable to complement a virB8 mutant and displayed a dominant negative phenotype when expressed in wild type B. suis. We suggest that interaction of VirB8 with VirB10 could play a major role in the correct function of the B. suis VirB T4SS. Structured summary of protein interactions:AtVirB8 physically interacts with AtVirB10 by two hybrid (View interaction) TraJ physically interacts with TraJ by two hybrid (View Interaction 1, 2) AtVirB8 physically interacts with AtVirB8 by two hybrid (View interaction) VirB10 physically interacts with VirB10 by two hybrid (View interaction) VirB8 physically interacts with VirB8 by two hybrid (View Interaction 1, 2) VirB10 physically interacts with VirB8 by two hybrid (View interaction) AtVirB10 physically interacts with AtVirB10 by two hybrid (View interaction) VirB8 physically interacts with VirB10 by two hybrid (View interaction) AtVirB10 physically interacts with AtVirB8 by two hybrid (View interaction)