Poster Presentation The 43rd Lorne Conference on Protein Structure and Function 2018

A Nightmare on EM Street: structural determination of the AAA ATPase Vps4 oligomer (#105)

Lou Brillault 1 , Andrew Whitten 2 , Mohamed Chami 3 , Kenneth Goldie 3 , Henning Stahlberg 3 , Michael Landsberg 4
  1. Institute for Molecular Bioscience, St Lucia, QLD, Australia
  2. Australian Nuclear Science and Technology Organisation, Sydney, NSW, Australia
  3. Center for Cellular Imaging and Nano-Analytics, Biozentrum, The University of Basel, Basel, Switzerland
  4. School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD, Australia

The vacuolar protein sorting-associated protein 4 (Vps4) AAA ATPase is a key regulator of a group of multifunctional complexes known as endosomal sorting complexes required for transport (ESCRTs). ESCRTs characteristically control the formation of multivesicular bodies in eukaryotic cells and have subsequently been implicated in a variety of cellular membrane remodelling events that require the formation of an outward facing bud, including cytokinetic abscission, viral budding and the repair of plasma membrane lesions. In these processes, Vps4 catalyses the recycling of membrane-associated ESCRT-III components away from the budding membrane – a step that is a perquisite to membrane fission. The Vps4 holoenzyme is a homo-oligomeric species, activated upon ATP binding. The structure of oligomeric Vps4 has been the subject of considerable controversy, largely due to the fact that the wild type enzyme only forms a transient oligomer, while a hydrolysis-deficient point mutant (Vps4E233Q) has been claimed to induce an inactive structure. Presented here is a 7.9 Å resolution cryo-EM structure of Vps4E233Q. These studies highlight the challenges encountered in the characterization of this recalcitrant system using cryo-EM. This structure indicates that Vps4, like other AAA ATPases, forms an asymmetric, hexameric ring resembling a “notched-washer”. Taken together with recent reports, these data suggest that Vps4E233Q does form a physiologically relevant structure. However, SAXS data suggest that Vps4 also forms higher order structures (>6mer), with Vps4E233Q appearing to exhibit a greater propensity to form these. In the case of Vps4, the physiological relevance of these higher orders structures remains to be established, underlining the need for caution when employing Vps4E233Q as a model for the wild type holoenzyme.