Structural Identification of the Vps18 beta-Propeller Reveals a Critical Role in the HOPS Complex Stability and Function

Abstract

Membrane fusion at the vacuole, the lysosome equivalent in yeast, requires the HOPS tethering complex, which is recruited by the Rab7 GTPase Ypt7. HOPS provides a template for the assembly of SNAREs and thus likely confers fusion at a distinct position on vacuoles. Five of the six subunits in HOPS have a similar domain prediction with strong similarity to COPII subunits and nuclear porins. Here, we show that Vps18 indeed has a seven-bladed beta-propeller as its N-terminal domain by revealing its structure at 2.14 angstrom. The Vps18 N-terminal domain can interact with the N-terminal part of Vps11 and also binds to lipids. Although deletion of the Vps18 N-terminal domain does not preclude HOPS assembly, as revealed by negative stain electron microscopy, the complex is instable and cannot support membrane fusion in vitro. We thus conclude that the beta-propeller of Vps18 is required for HOPS stability and function and that it can serve as a starting point for further structural analyses of the HOPS tethering complex.