Baldwin, A. | Search bioRxiv

bioRxiv2018

Glucocerebrosidase rescues alpha-synuclein from amyloid formation

Aggregation of the protein -synuclein (Syn) Into amyloid fibrils is associated with Parkinsons disease (PD), a process accelerated by lipids. Recently, the lysosomal protein glucocerebrosidase (GCase) has been identified as a major risk factor in both genetic and sporadic PD. Here, we use solution state NMR to reveal that GCase directly inhibits lipid induced Syn amyloidogenesis. Structurally, we show that the mechanism for this requires competition between lipids and GCase for Syn, binding the N and C termini respectively. The affinity of GCase for the C-terminus of Syn is such that not only does it inhibit lipid induced amyloid formation, but also it destabilizes mature Syn amyloid fibrils. These results reveal a competitive molecular \"tug-of-war\" for Syn termini by GCase and lipid, providing a mechanistic link between the clinically observed links between changes in GCase abundance and Parkinsons disease.

biophysics↗

bioRxiv2018

Phosphorylation of HspB1 regulates its mechanosensitive molecular chaperone interaction with native filamin C

Small heat-shock proteins (sHsps; HspBs) are molecular chaperones involved in the cellular stress response and a range of basal functions. Despite a multitude of targets, sHsp interactions are not well understood due their heterogeneous structures and weak binding affinities. The most widely expressed human sHsp, HspB1, is prevalent in striated muscle, where the actin cross-linker filamin C (FLNC, {gamma}-filamin, ABP-L) is a putative binding partner. Musculoskeletal HspB1 is phosphorylated in response to a variety of cues, including mechanical stress, which promotes oligomer disassembly and association with myoarchitectural elements. Here, we report the up-regulation and interaction of both proteins in the hearts of a mouse model of heart failure, with HspB1 being phosphorylated and FLNC increasingly associated with the sarcomeric Z-disc. We used a combination of structural approaches to reveal that phosphorylation of HspB1 results in increased availability of the residues surrounding the phosphosite, facilitating their interaction with folded FLNC domains equivalent to a force-sensing region in the paralog filamin A. By employing native mass spectrometry, we show that domains 18 to 21 of FLNC are extensible under conditions mimicking force, with phosphorylated HspB1 stabilising an intermediate from further unfolding. These findings report on conformations accessible during the cycles of mechanical extension central to filamin function, and are consistent with an interaction between the chaperone and a native target that is strengthened upon the application of force. This may represent a new mode of molecular chaperone activity, allowing HspB1 to protect FLNC from over-extension during mechanical stress.

biophysics↗