This is the C-terminal domain of Vta1 proteins Pfam:PF04652 . Structural and functional analysis indicate that this C-terminal domain promotes the ATP-dependent double ring assembly of Vps4. Furthermore, it has been shown that it is necessary and sufficient for protein dimerization. Mutations in Lys-299 and Lys-302 completely abolished the ability of Vta1 to stimulate the ATPase activity of Vps4 while mutation in Lys-322 had no effect [1].

1: Structural basis of Vta1 function in the multivesicular body sorting pathway. Xiao J, Xia H, Zhou J, Azmi IF, Davies BA, Katzmann DJ, Xu Z; Dev Cell. 2008;14:37-49. PMID:18194651

2: Structural role of the Vps4-Vta1 interface in ESCRT-III recycling. Yang D, Hurley JH; Structure. 2010;18:976-984. PMID:20696398