Abstract
Congenital mutations in human small heat shock protein HSPB1 (HSP27) have been linked to Charcot-Marie-Tooth disease, a commonly occurring peripheral neuropathy. Understanding the molecular mechanism of such mutations is indispensable towards developing future therapies for this currently incurable disorder. Here we describe the physico-chemical properties of the autosomal dominant HSPB1 mutants R127W, S135F and R136W. Despite having a nominal effect on thermal stability, the three mutations induce dramatic changes to quaternary structure. At high concentrations or under crowding conditions, the mutants form assemblies that are approximately two times larger than those formed by the wild-type protein. At low concentrations, the mutants have a higher propensity to dissociate into small oligomers, while the dissociation of R127W and R135F mutants is enhanced by MAPKAP kinase-2 mediated phosphorylation. Specific differences are observed in the ability to form hetero-oligomers with the homologue HSPB6 (HSP20). For wild-type HSPB1 this only occurs at or above physiological temperature, whereas the R127W and S135F mutants form hetero-oligomers with HSPB6 at 4 °C, and the R136W mutant fails to form hetero-oligomers. Combined, the results suggest that the disease-related mutations of HSPB1 modify its self-assembly and interaction with partner proteins thus affecting normal functioning of HSPB1 in the cell.
Highlights
Inherited peripheral neuropathies are a genetically diverse group of neurodegenerative disorders that affect the function and survival of motor or sensory neurons in the peripheral nervous system[1,2]
In agreement with the small angle X-ray scattering (SAXS) experiments, the wild type (WT) HSPB1 had a sedimentation coefficient of 15.8 S, whereas the R127W, S135F, R136W mutants were considerably larger with sedimentation coefficients of 23.1, 20.8 and 24.3 S, respectively. These results show that the three HSPB1 mutants studied form nearly spherical oligomers composed of more subunits than the WT protein but with a comparable packing density
We have analyzed the effect that three autosomal dominant mutations of human HSPB1 linked to the CMT2 disease have on the physico-chemical properties of this small heat shock proteins (sHSPs)
Summary
Inherited peripheral neuropathies are a genetically diverse group of neurodegenerative disorders that affect the function and survival of motor or sensory neurons in the peripheral nervous system[1,2] Amongst this clinically heterogeneous group, Charcot-Marie-Tooth (CMT) disease is the most common, with a reported incidence of 1 in 2500 individuals[2]. It was speculated that these mutants are hyperactive due to their increased monomerization resulting in a more effective and tighter interaction with different target proteins[22] This has led to a model whereby the altered binding properties of these HSPB1 mutants to tubulin and the microtubule deacetylase HDAC6 may affect the stability and remodeling of microtubules, as well as disrupt transport along these cytoskeletal elements. These processes are essential in neurons, which explain the fact that the mutations lead to neurodegeneration[23,24]
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