Inter-Subunit Coordination in Hsp104, a Protein Disaggregase

Abstract

Hsp104, a hexameric AAA+ ATPase from yeast, disaggregates diverse structures including stress-induced amorphous aggregates, yeast prions, and disease associated amyloid conformers. However, the mechanism by which these substrates are remodeled is unknown. We have shown that Hsp104 hexamers adapt different mechanisms of intersubunit collaboration to disaggregate amorphous aggregates versus amyloid. To resolve amorphous aggregates, Hsp104 subunits collaborate non-co-operatively via probabilistic substrate binding and ATP hydrolysis. To disaggregate amyloid, several subunits co-operatively engage substrate and hydrolyze ATP. We also found that inter-subunit co-operativity is dictated by the stability of the substrate: Hsp104 hexamers deploy more subunits to disaggregate Sup35 prion strains with more stable ‘cross-β' cores. Surprisingly, the mechanism of inter-subunit co-operativity is not conserved, as the prokaryotic homologue of Hsp104, ClpB, collaborates differently than Hsp104 and couples probabilistic substrate binding to co-operative ATP hydrolysis.