A weakened interface in the P182L variant of HSP27 associated with severe Charcot‐Marie‐Tooth neuropathy causes aberrant binding to interacting proteins

Abstract

HSP27 is a human molecular chaperone that forms large, dynamic oligomers and functions in many aspects of cellular homeostasis. Mutations in HSP27 cause Charcot‐Marie‐Tooth (CMT) disease, the most common inherited disorder of the peripheral nervous system. A particularly severe form of CMT disease is triggered by the P182L mutation in the highly conserved IxI/V motif of the disordered C‐terminal region, which interacts weakly with the structured core domain of HSP27. Here, we observed that the P182L mutation disrupts the chaperone activity and significantly increases the size of HSP27 oligomers formed in vivo, including in motor neurons differentiated from CMT patient‐derived stem cells. Using NMR spectroscopy, we determined that the P182L mutation decreases the affinity of the HSP27 IxI/V motif for its own core domain, leaving this binding site more accessible for other IxI/V‐containing proteins. We identified multiple IxI/V‐bearing proteins that bind with higher affinity to the P182L variant due to the increased availability of the IxI/V‐binding site. Our results provide a mechanistic basis for the impact of the P182L mutation on HSP27 and suggest that the IxI/V motif plays an important, regulatory role in modulating protein–protein interactions.

Induced pluripotent stem cell-derived motor neurons of CMT type 2 patients reveal progressive mitochondrial dysfunction

“…A second example of a gene-specific phenotype is the formation of HSPB1-positive aggregates due to C-terminal HSPB1 mutations. 21 We validated the presence of HSPB1 aggregates in our iPSC-derived motor neurons from the HSPB1 P182L line, using immunostaining at Day 37 for HSPB1 ( Supplementary Fig. 3 A).…”

Insights on Human Small Heat Shock Proteins and Their Alterations in Diseases

“…Since the major aspect regulating HSPB1 activity relies on its self-association and dissociation, dimerization and oligomerization dynamics have been investigated as one of the primary features possibly altered in the mutant protein. In vitro, biochemical studies on HSPB1 mutations falling in different regions of the protein sequence revealed a common tendency to form larger oligomers, often accompanied by a decreased chaperone activity in respect to the HSPB1 wild-type (WT); in vitro analyses also reported a destabilization of the quaternary structure of mutated HSPB1 (Nefedova et al, 2013a;Nefedova et al, 2013b;Chalova et al, 2014b;Muranova et al, 2015;Alderson et al, 2021). Clustering HSPB1 mutations through a domain-dysfunction linkage is not unequivocal, due to contrasting observations resulted from different techniques and assays used to study mutations localized in the same HSPB1 region (Almeida-Souza et al, 2010;Ylikallio et al, 2015;Echaniz-Laguna et al, 2017a).…”

Insights Into the Role of Heat Shock Protein 27 in the Development of Neurodegeneration

“…Another structurally notable feature of the ACD is the β4/β8 groove which includes a hydrophobic pocket centered between β-strands 4 and 8 and is located on the outer edge of the ACD β-sandwich (Ehrnsperger et al, 1997 ; Klevit, 2020 ; Reid Alderson et al, 2021 ; Figure 3C ). Therefore, within a dimer of Hsp27 there are two hydrophobic grooves located at the edges of each monomer and one shared dimer interface groove created by the linkage of two monomers (Clouser et al, 2019 ; Boelens, 2020 ; Figure 3D ).…”

“…This is described as an extended formation of the CTR in the trans-conformation as the canonical proline can undergo cis-trans isomerization about the I-P peptide bond (Alderson et al, 2017 ). The interaction is found to occur within the same dimeric subunit and between adjacent dimers as well (Reid Alderson et al, 2021 ). The lowly populated residual β-strand structure may further encourage binding between the ACD and CTR and other binding partners (Alderson et al, 2017 ).…”

“…The lowly populated residual β-strand structure may further encourage binding between the ACD and CTR and other binding partners (Alderson et al, 2017 ). The IXI/V motif is considered a short linear motif (SLiM) that modulates interactions between proteins (Reid Alderson et al, 2021 ). In the case of Hsp27, those interactions are between the CTR, the ACD, and possibly client proteins (Reid Alderson et al, 2021 ).…”