This conserved domain is found in Xanthomonas VirD4 interacting proteins (XVIPs) and other type IV secretion system (T4SS) specialised in translocating effector proteins (toxic effector proteins, X-Tfes) into competing gram-negative species, leading to target cell death. This domain interacts with the central all-alpha domain of VirD4. Its structure shows two well ordered N-terminal antiparallel alpha-helices that pack against a carboxyl-terminal three-stranded antiparallel beta sheet [1-3].

1: Identification of new protein-protein interactions involving the products of the chromosome- and plasmid-encoded type IV secretion loci of the phytopathogen Xanthomonas axonopodis pv. citri. Alegria MC, Souza DP, Andrade MO, Docena C, Khater L, Ramos CH, da Silva AC, Farah CS; J Bacteriol. 2005;187:2315-2325. PMID:15774874

2: Bacterial killing via a type IV secretion system. Souza DP, Oka GU, Alvarez-Martinez CE, Bisson-Filho AW, Dunger G, Hobeika L, Cavalcante NS, Alegria MC, Barbosa LR, Salinas RK, Guzzo CR, Farah CS; Nat Commun. 2015;6:6453. PMID:25743609

3: Structural basis for effector recognition by an antibacterial type IV secretion system. Oka GU, Souza DP, Cenens W, Matsuyama BY, Cardoso MVC, Oliveira LC, da Silva Lima F, Cuccovia IM, Guzzo CR, Salinas RK, Farah CS; Proc Natl Acad Sci U S A. 2022; [Epub ahead of print] PMID:34983846