Residue R120 Is Essential for the Quaternary Structure and Functional Integrity of Human RB-Crystallin†

International audienceThe missense mutation Arg-120 to Gly (R120G) in the human RΒ-crystallin sequence has been reported to be associated with autosomal dominant myopathy, cardiomyopathy, and cataract. Previous studies of the mutant showed a significant ability to aggregate in cultured cells and an increased oligomeric size coupled to an important loss of the chaperone-like activity in Vitro. The aim of this study was to further analyze the role of the R120 residue in the structural and functional properties of RΒ-crystallin. The following mutants were generated, Arg-120 to Gly (R120G), Cys (R120C), Lys (R120K), and Asp (R120D). In cellulo, after expression in two cultured cell lines, NIH-3T3 and Cos-7, the capacity of the wild-type and mutant crystallins to aggregate was evaluated and the protein location was determined by immunofluorescence. In Vitro, the wild-type and mutant crystallins were expressed in Escherichia coli cells, purified by size exclusion chromatography, and characterized using dynamic light scattering, electron microscopy, and chaperone-like activity assays. Aggregate sizes in cellulo and in Vitro were analyzed. The whole of the data showed that the preservation of an Arg residue at position 120 of RΒ-crystallin is critical for the structural and functional integrity of the protein and that each mutation results in specific changes in both structural and functional characteristics