THE STRUCTURAL BASIS FOR POLYPEPTIDE TRANSLOCATION BY THE HSP104 DISAGGREGASE

Abstract

Heat shock protein (Hsp) 104, found in yeast, is a member of the Hsp100 class of molecular chaperones that contain highly conserved AAA+ (ATPases Associated with diverse cellular Activities) domains and serve critical roles in thermotolerance and protein quality control. Hsp104, and the bacterial homolog ClpB, form large hexameric‐ring structures that cooperate with the Hsp70 system to unfold and rescue aggregated protein states by active translocation of polypeptide substrates through a central channel. Hsp104 controls prion inheritance in yeast by recognizing and remodeling cross‐β structures of amyloid fibrils, such as those found in Sup35 prions. This function has led to studies identifying potentiated Hsp104 variants that reduce the toxicity of proteins linked to neurodegenerative diseases. Despite fundamental roles in protein quality control and promising therapeutic activity in rescuing amyloidogenic states, how Hsp104 and its family members function as powerful molecular motors to solubilize proteins is not fully understood. Furthermore, obtaining high‐resolution views of active complexes has been a significant challenge, thus a definitive structural mechanism for disaggregation has remained elusive. Here we have determined the cryo‐EM structure of wild type Hsp104 in the ATP state to 5.6 Å resolution. This work reveals an unprecedented two‐turn spiral architecture for the hexamer, identifying how the twelve AAA+ domains are coordinated for substrate translocation. The N‐terminal, C‐terminal and middle domains are observed in distinct conformations that explain functions in substrate engagement and ATP hydrolysis control. Remarkably, density for the substrate‐binding pore loops is identified to line the channel in a continuous arrangement that appears optimized for substrate transfer across the AAA+ domains, establishing a directional path for polypeptide translocation.Support or Funding InformationThis work was supported by National Institutes of Health (NIH) grant R01GM099836 (to J.S.). A.L.Y. is supported by an American Heart Association Predoctoral fellowship; M.E.J. is supported by a Target ALS Springboard Fellowship. J.S. is supported by a Muscular Dystrophy Association Research Award (MDA277268), the Life Extension Foundation, the Packard Center for ALS Research at Johns Hopkins University, and Target ALS. D.R.S. is supported by NIH grants R01GM109896, R01GM077430 and R01GM110001A.