Oligomerization and chaperone-like activity of Drosophila melanogaster small heat shock protein DmHsp27 and three arginine mutants in the alpha-crystallin domain
The small Hsp DmHsp27 from Drosophila melanogaster is one of the few small heat shock proteins (sHsps) found within the nucleus. We report that its dimerization is independent of disulfide bond formation and seems to rely on salt bridges. Unlike metazoan sHsps, DmHsp27 forms two populations of oligomers not in equilibrium. Mutations at highly conserved arginine residues in mammalian sHsps have been reported to be associated with protein conformational defects and intracellular aggregation. Independent mutation of three highly conserved arginines (R122, R131, and R135) to glycine in DmHsp27 results in only one population of higher molecular weight form. In vitro, the chaperone-like activity of wild-type DmHsp27 was comparable with that of its two isolated populations and to the single population of the R122G, R131G, and R135G using luciferase as substrate. However, using insulin, the chaperone-like activity of wild-type DmHsp27 was lower than that of R122G and R131G mutants. Altogether, the results characterize wild-type DmHsp27 and its alpha-crystallin domain (ACD) arginine mutants and may give insight into protection mechanism of sHsps.
KeywordsSmall heat shock protein (sHsp) DmHsp27 Chaperone Alpha-crystallin domain (ACD) Drosophila melanogaster
We would like to thank Jérémie Hamel from the Institute for Integrative Systems Biology (IBIS) for help with SEC, Fériel Skouri-Panet from the Institute of Mineralogy, Materials Physics and Cosmochemistry, and Ahmed Haouz from the crystallogenesis platform at the Pasteur Institute for technical help. This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to RMT. MTM held a studentship from PROTEO, Québec.
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