Bro1 binding to Snf7 regulates ESCRT-III membrane scission activity in yeast

Endosomal sorting complexes required for transport (ESCRTs) promote the invagination of vesicles into the lumen of endosomes, the budding of enveloped viruses, and the separation of cells during cytokinesis. These processes share a topologically similar membrane scission event facilitated by ESCRT-III assembly at the cytosolic surface of the membrane. The Snf7 subunit of ESCRT-III in yeast binds directly to an auxiliary protein, Bro1. Like ESCRT-III, Bro1 is required for the formation of intralumenal vesicles at endosomes, but its role in membrane scission is unknown. We show that overexpression of Bro1 or its N-terminal Bro1 domain that binds Snf7 enhances the stability of ESCRT-III by inhibiting Vps4-mediated disassembly in vivo and in vitro. This stabilization effect correlates with a reduced frequency in the detachment of intralumenal vesicles as observed by electron tomography, implicating Bro1 as a regulator of ESCRT-III disassembly and membrane scission activity.