A novel mechanism of engagement of Hsp70 with α-synuclein provides specific therapeutic opportunities
Jihau Tao2, Amandine Berthet1, Robert Stanley1, David Agard2, Lisa McConlogue1,2 1Gladstone Institute of Neurological Disease, 2 Department of Biochemistry and Biophysics, University of California, San Francisco
The pathogenic misfolding of alpha-Synuclein (ASyn) is central to the onset and progression of Parkinson's disease (PD) and related synucleinopathies. These diseases cause debilitating symptoms yet no treatment slows their inexorable decline. The stress induced chaperone Hsp70 protects against ASyn misfolding and pathogenicity, yet the assumption that this protection is mediated by the canonical and promiscuous mode of Hsp70 action with its associated untoward effects has stymied mechanistic investigation. We have identified a novel, non-canonical molecular mechanism of Hsp70 preventing ASyn misfolding which offers a potentially specific mechanism of Hsp70 protection in disease. Notably our biochemical data indicate that Hsp70 can block the earliest and likely pathogenic stages of ASyn misfolding, ASyn oligomerization, by a surprising mechanism separable from its normal substrate binding site. Using a novel ASyn oligomerization biochemical assay we show that Hsp70 blocking ASyn oligomerization is neither dependent on the ATP cycling required for canonical action nor on the entire Hsp70 N-terminal nucleotide binding domain. Importantly, an inhibitor of the canonical Hsp70 substrate binding site does not prevent Hsp70 impairment of ASyn oligomerization indicating that ASyn interacts at an alternative site. Because this interaction can be separated from Hsp70's interaction with its myriad of canonical substrates, it holds potential for specific therapeutic targeting of Hsp70. Based on these data, we hypothesize that Hsp70 blocking of ASyn oligomerization via this novel, non-canonical interaction protects against ASyn pathogenicity. We are establishing cellular models to test this hypothesis and biochemical assays amenable for high throughput screening to identify small molecules modulating this engagement.
We are grateful for funding of this work by the Rogers Family Foundation via a QB3 Bridging the Gap Award, and especially appreciative of the attention and efforts of Gary Rogers and his family.