Involved in the endosomal multivesicular bodies (MVB) pathway. MVBs contain intraluminal vesicles (ILVs) that are generated by invagination and scission from the limiting membrane of the endosome and are delivered to lysosomes enabling degradation of membrane proteins. Thought to be a cofactor of VPS4, which catalyzes the disassembly of membrane-associated ESCRT-III (By similarity). Belongs to the VTA1 family.