Ghazi-Tabatabai Sara, Saksena Suraj, Short Judith M, Pobbati Ajaybabu V, Veprintsev Dmitry B, Crowther R Anthony, Emr Scott D, Egelman Edward H, Williams Roger L
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.
Structure. 2008 Sep 10;16(9):1345-56. doi: 10.1016/j.str.2008.06.010.
The ESCRT machinery mediates sorting of ubiquitinated transmembrane proteins to lysosomes via multivesicular bodies (MVBs) and also has roles in cytokinesis and viral budding. The ESCRT-III subunits are metastable monomers that transiently assemble on membranes. However, the nature of these assemblies is unknown. Among the core yeast ESCRT-III subunits, Snf7 and Vps24 spontaneously form ordered polymers in vitro. Single-particle EM reconstruction of helical Vps24 filaments shows both parallel and head-to-head subunit arrangements. Mutations of regions involved in intermolecular assembly in vitro result in cargo-sorting defects in vivo, suggesting that these homopolymers mimic interactions formed by ESCRT-III heteropolymers during MVB biogenesis. The C terminus of Vps24 is at the surface of the filaments and is not required for filament assembly. When this region is replaced by the MIT-interacting motif from the Vps2 subunit of ESCRT-III, the AAA-ATPase Vps4 can both bundle and disassemble the chimeric filaments in a nucleotide-dependent fashion.
内体分选转运复合体（ESCRT）机制通过多泡体（MVBs）介导泛素化跨膜蛋白分选至溶酶体，并且在胞质分裂和病毒出芽过程中也发挥作用。ESCRT-III亚基是亚稳态单体，可在膜上短暂组装。然而，这些组装体的性质尚不清楚。在酵母ESCRT-III核心亚基中，Snf7和Vps24在体外可自发形成有序聚合物。螺旋状Vps24细丝的单颗粒电子显微镜重建显示了平行和头对头的亚基排列。体外分子间组装相关区域的突变在体内导致货物分选缺陷，这表明这些同聚物模拟了ESCRT-III异聚物在MVB生物发生过程中形成的相互作用。Vps24的C末端位于细丝表面，细丝组装不需要该区域。当该区域被ESCRT-III的Vps4中与MIT相互作用的基序取代时，AAA-ATP酶Vps4可以以核苷酸依赖的方式使嵌合细丝成束和解聚。
