Characterization of Mutants of Human Small Heat Shock Protein HspB1 Carrying Replacements in the N-Terminal Domain and Associated with Hereditary Motor Neuron Diseases: e0126248

• Published in: PloS one 2015-05, Vol.10 (5)
• Main Authors: Muranova, Lydia K, Weeks, Stephen D, Strelkov, Sergei V, Gusev, Nikolai B
• Format: Article
• Language: English
• ISSN: 1932-6203
• DOI: 10.1371/journal.pone.0126248

Physico-chemical properties of the mutations G34R, P39L and E41K in the N-terminal domain of human heat shock protein B1 (HspB1), which have been associated with hereditary motor neuron neuropathy, were analyzed. Heat-induced aggregation of all mutants started at lower temperatures than for the wild type protein. All mutations decreased susceptibility of the N- and C-terminal parts of HspB1 to chymotrypsinolysis. All mutants formed stable homooligomers with a slightly larger apparent molecular weight compared to the wild type protein. All mutations analyzed decreased or completely prevented phosphorylation-induced dissociation of HspB1 oligomers. When mixed with HspB6 and heated, all mutants yielded heterooligomers with apparent molecular weights close to ~400 kDa. Finally, the three HspB1 mutants possessed lower chaperone-like activity towards model substrates (lysozyme, malate dehydrogenase and insulin) compared to the wild type protein, conversely the environmental probe bis-ANS yielded higher fluorescence with the mutants than with the wild type protein. Thus, in vitro the analyzed N-terminal mutations increase stability of large HspB1 homooligomers, prevent their phosphorylation-dependent dissociation, modulate their interaction with HspB6 and decrease their chaperoning capacity, preventing normal functioning of HspB1.