N- and C-terminal regions of αB-crystallin and Hsp27 mediate inhibition of amyloid nucleation, fibril binding, and fibril disaggregation

Abstract

Small heat-shock proteins (sHSPs) are ubiquitously expressed molecular chaperones that inhibit amyloid fibril formation; however, their mechanisms of action remain poorly understood. sHSPs comprise a conserved α-crystallin domain flanked by variable N- and C-terminal regions. To investigate the functional contributions of these three regions, we compared the chaperone activities of various constructs of human αB-crystallin (HSPB5) and heat-shock 27-kDa protein (Hsp27, HSPB1) during amyloid formation by α-synuclein and apolipoprotein C-II. Using an array of approaches, including thioflavin T fluorescence assays and sedimentation analysis, we found that the N-terminal region of Hsp27 and the terminal regions of αB-crystallin are important for delaying amyloid fibril nucleation and for disaggregating mature apolipoprotein C-II fibrils. We further show that the terminal regions are required for stable fibril binding by both sHSPs and for mediating lateral fibril–fibril association, which sequesters preformed fibrils into large aggregates and is believed to have a cytoprotective function. We conclude that although the isolated α-crystallin domain retains some chaperone activity against amyloid formation, the flanking domains contribute additional and important chaperone activities, both in delaying amyloid formation and in mediating interactions of sHSPs with amyloid aggregates. Both these chaperone activities have significant implications for the pathogenesis and progression of diseases associated with amyloid deposition, such as Parkinson's and Alzheimer's diseases.

Spatially resolved transcriptomics reveals unique gene signatures associated with human temporal cortical architecture and Alzheimer’s pathology

“…7). Interestingly, CRYAB (HSPB5) has been found to mediate the inhibition of amyloid nucleation, fibril binding, and fibril disaggregation 58 . The upregulation of oligodendrocyte-related genes has been demonstrated in AD-like animals and human AD at the early stages of the disease 10, 13, 30 .…”

Could Small Heat Shock Protein HSP27 Be a First-Line Target for Preventing Protein Aggregation in Parkinson’s Disease?

“…There is growing evidence that HSP27 is involved in the cellular response to protein aggregation in a variety of neurodegenerative diseases, and the intra- or extra-aggregation of specific proteins to form amyloid fibrils is a pathological hallmark of neurodegenerative diseases, such as PD [ 72 ]. α-synuclein is one example of a protein that forms fibrils and insoluble deposits both in vitro and in vivo, being highly expressed in multiple regions of the brain, mainly in dopaminergic neurons in the SNpc of PD patients [ 73 ].…”

“…However, ACD alone is not sufficient for all of the chaperone‘s activities exhibited by the full-length protein. Recently, it has been demonstrated that N- and C-terminal regions, as well as the ACD of HSP27, mediate inhibition of amyloid nucleation, fibril binding, and fibril disaggregation [ 72 ]. HSP27 not only inhibits fibril elongation, but also reduces the cytotoxicity of fibrils, either by coating the aggregates and reducing their reactive surface area [ 87 ] or by sequestering them into larger inclusion body-like structures [ 88 ].…”

Secreted Chaperones in Neurodegeneration

“…Through partial unfolding, sometimes in response to environmental stressors ( Kirbach and Golenhofen, 2011 ; Alderson et al, 2020 ), they are able to interact with a variety of client proteins (reviewed in Webster et al, 2019 ). Supportive of an extracellular role in proteostasis, HspB5, also known as alpha crystallin, αBC, and CRYAB, has long been known as a potent anti-aggregant in vitro against a variety of fibrillating proteins; these studies span the last two decades [recently reviewed in Boelens (2020) ; see also Selig et al (2020) and Bendifallah et al (2020) for recent results concerning Abeta and synuclein, respectively].…”