Résumé :
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Three mutations (R120G, Q151X, 464?CT) in the small heat shock protein (sHsp) ?B-crystallin (?BC) have been found to cause inherited myofibrillar myopathy (Selcen and Engel, 2003; Vicart et al., 1998). ?BC forms homo-dimers, hetero-dimers with other sHsps, and larger oligomers. In an effort to elucidate the molecular basis for the associated myopathy, we have determined for these mutant ?BC proteins i) the formation of aggregates in transfected cells, ii) the partition into different subcellular fractions, iii) the phosphorylation status, and iv) the ability to interact with themselves, with wild-type ?BC, and with other sHsps that are abundant in muscles. We found that all 3 ?BC mutants have an increased tendency to form cytoplasmic aggregates in transfected cells and significantly increased levels of phosphorylation when compared to the wild-type protein. While wild-type ?BC partitioned essentially into the cytosol and membranes/organelles fractions, mutant ?BC proteins partitioned additionally into the nuclear and cytoskeletal fractions. Using various protein interaction assays, including quantitative fluorescence resonance energy transfer measurements in live cells, we found abnormal interactions of the various ?BC mutants with wild-type ?BC, themselves and the other sHsps Hsp20, Hsp22, and possibly with Hsp27. The collected data suggest that each ?BC mutant has a unique pattern of abnormal interaction properties (Simon et al., 2007). These distinct properties of the ?BC mutants identified are likely to contribute to a better understanding of the gradual manifestation and clinical heterogeneity of the associated myopathy in patients . Selcen, D. et al (2003). Myofibrillar myopathy caused by novel dominant negative alpha B-crystallin mutations. Ann Neurol Simon, S. et al (2007). Myopathy-associated alpha B-crystallin mutants: Abnormal phosphorylation, intracellular location, and interactions with other small heat shock proteins. J Biol Chem. Vicart, P. et al. (1998). A missense mutation in the alphaB-crystallin chaperone gene causes a desmin-related myopathy. Nat Genet.
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