Tai4 is a new form of autoimmunity protein for a type VI secretion system, T6SS. T6SS has roles in interspecies interactions, as well as higher order host-infection, by injecting effector proteins into the periplasmic compartment of the recipient cells of closely related species. Pseudomonas aeruginosa produces at least three effector proteins to other cells and thus has three specific cognate immunity proteins to protect itself. Tae4, or type VI amidase effector 4, in Enterobacter cloacae has a cognate Tai4 or type VI amidase immunity 4 protein [1]. The effector is Tae4, Pfam:PF14113.

1: Structure of the type VI effector-immunity complex (Tae4-Tai4) provides novel insights into the inhibition mechanism of the effector by its immunity protein. Zhang H, Zhang H, Gao ZQ, Wang WJ, Liu GF, Xu JH, Su XD, Dong YH; J Biol Chem. 2013;288:5928-5939. PMID:23288853