Antitoxin TsiV3, also known as TsaB, is a immmunity protein from Vibrio cholerae that inhibits the activity of toxin VgrG3, a protein found in the spike of the type VI secretion system (T6SS) syringe- like complex. TsiV3 folds into a three-helix bundle and adopts a dimeric assembly to bind the deep active-site groove of the catalytic domain in the C-terminal region of VgrG3, modifying the conformation and preventing substrate binding [1-3].

1: Molecular mechanism for self-protection against the type VI secretion system in Vibrio cholerae. Yang X, Xu M, Wang Y, Xia P, Wang S, Ye B, Tong L, Jiang T, Fan Z; Acta Crystallogr D Biol Crystallogr. 2014;70:1094-1103. PMID:24699653

2: Structural basis for recognition of the type VI spike protein VgrG3 by a cognate immunity protein. Zhang J, Zhang H, Gao Z, Hu H, Dong C, Dong YH; FEBS Lett. 2014;588:1891-1898. PMID:24751834

3: Dual expression profile of type VI secretion system immunity genes protects pandemic Vibrio cholerae. Miyata ST, Unterweger D, Rudko SP, Pukatzki S; PLoS Pathog. 2013;9:e1003752. PMID:24348240