Structural and Functional Regulation of Vps4 by ESCRT Proteins.

[摘要] The Endosomal Sorting Complexes Required for Transport (ESCRT) machinery controls key cellular processes, including multivesicular body (MVB) biogenesis, retroviral release, division between daughter cells, and closure of small plasma membrane wounds, all of which require the budding of membrane away from the cytosol.The ESCRT proteins function by binding membrane, generating curvature, and through the enzymatic activity of an AAA-ATPase Vps4, executing membrane scission.Both the localization and oligomerization state of Vps4 are important mechanisms that control Vps4 activity.The ESCRT-III proteins are themselves substrates of Vps4 activity but also participate in regulating Vps4 function.These proteins are structurally related, and contain a unique protein-interaction motif known as the MIT-interacting motif (MIM) that engages the Vps4 microtubule-interacting and trafficking (MIT) domain.Through this MIT-MIM interaction, the ESCRT-III proteins are thought to drive oligomerization and recruit Vps4 to the site of action.Vps4 regulation is further expanded by its co-factor Vta1, which itself contains two tandem MIT domains that bind to the ESCRT-III proteins.Two yeast ESCRT-III proteins, Did2 and Vps60, were initially found to bind the second Vta1 MIT domain that stimulates Vps4 via Vta1 binding.Biochemical analysis showed that Did2 does not bind to the second MIT domain as previously thought, but in fact binds to the first MIT domain.The crystal structure of the LIP5-CHMP1B complex (human orthologs of Vta1 and Did2) showed that this mode of interaction is conserved.Interestingly, the binding interface of Vps60 to Vta1 has diverged in higher species.It appears that LIP5 has evolved different structural requirements for VPS4 stimulation as well, and that CHMP5 (human ortholog of Vps60) has also gained an inhibitory function for LIP5 stimulation, which is in contrast to yeast Vps60.Another interesting difference between the human and yeast systems is that yeast harbor a novel ESCRT-III protein Vfa1.Vfa1 regulates Vps4 through a high-affinity MIT-MIM interaction that can greatly stimulate Vps4 ATPase activity.Taken together, these results suggest that while the basic mechanism of ESCRT function is conserved, there is a significant divergence in the regulatory mechanism of ESCRT action, with Vps4 as a prime example.

[发布机构] University of Michigan

[效力级别] Vps4

[关键词] ESCRT;Vps4;Structural biology;protein-protein interactions;multivesicular bodies;Biological Chemistry;Science;Biological Chemistry