Conformational Changes in the Endosomal Sorting Complex Required for Transport-III Subunit Ist1 Lead to Distinct Modes of ATPase Vps4 Regulation [Enzymology]

October 29th, 2015 by Tan, J., Davies, B. A., Payne, J. A., Benson, L. M., Katzmann, D. J.

Intralumenal vesicle formation of the multivesicular body is a critical step in the delivery of endocytic cargoes to the lysosome for degradation. Endosomal Sorting Complex Required for Transport-III (ESCRT-III) subunits polymerize on endosomal membranes to facilitate membrane budding away from the cytoplasm to generate these intralumenal vesicles. The ATPase Vps4 remodels and disassembles ESCRT-III, but the manner in which Vps4 activity is coordinated with ESCRT-III function remains unclear. Ist1 is structurally homologous to ESCRT-III subunits and has been reported to inhibit Vps4 function despite the presence of a MIT-interacting motif (MIM) capable of stimulating Vps4 in the context of other ESCRT-III subunits. Here, we report that Ist1 inhibition of Vps4 ATPase activity involves two elements in Ist1: the MIM itself and a surface containing a conserved ELYC sequence. In contrast, the MIM interaction in concert with a more open conformation of the Ist1 core resulted in stimulation of Vps4. Addition of the ESCRT-III subunit binding partner of Ist1, Did2, also converted Ist1 from an inhibitor to a stimulator of Vps4 ATPase activity. Finally, distinct regulation of Vps4 by Ist1 corresponded with altered ESCRT-III disassembly in vitro. Together, these data support a model in which Ist1-Did2 interactions during ESCRT-III polymerization coordinate Vps4 activity with the timing of ESCRT-III disassembly.
  • Posted in Journal of Biological Chemistry, Publications
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