Molecular architecture and functional model of the complete yeast ESCRT-I heterotetramer

The endosomal sorting complex required for transport-1 (ESCRT-1) complex, which is conserved from yeast to humans, directs the lysosomal degradation of ubiquitinated transmembrane proteins and the budding of the HIV virus. Yeast ESCRT-1 contains four subunits, Vps23, Vps28, Vps37, and Mvb12. The crystal structure of the heterotetrameric ESCRT-1 complex reveals a highly asymmetric complex of 1:1:1:1 subunit stoichiometry. The core complex is nearly 18 nm long and consists of a headpiece attached to a 13 nm stalk. The stalk is important for cargo sorting by ESCRT-1 and is proposed to serve as a spacer regulating the correct disposition of cargo and other ESCRT components. Hydrodynamic constraints and crystallographic structures were used to generate a model of intact ESCRT-1 in solution. The results show how ESCRT-1 uses a combination of a rigid stalk and flexible tethers to interact with lipids, cargo, and other ESCRT complexes over a span of similar to 25 nm.