Protein-protein interactions between lens vimentin and αB-crystallin using FRET acceptor photobleaching

PURPOSE: The R120G mutation of αB-crystallin is known to cause desmin-related myopathy, but the mechanisms underlying the formation of cataract are not clearly established. We hypothesize that alteration of protein–protein interaction between R120G αB-crystallin and lens intermediate filament proteins is one of the mechanisms of congenital cataract. METHODS: Protein–protein interactions were determined by confocal fluorescence resonance energy transfer (FRET) microscopy using green fluorescence protein (GFP) as the donor and red fluorescence protein (RFP) as the acceptor. The lens vimentin gene was fused into a GFP vector and the αB-crystallin (WT or R120G mutant) gene was fused into the RFP vector. The donor-acceptor plasmid pairs of intermediate filament (IF)-GFP and αB-RFP were co-transfected into HeLa cells. After incubation, confocal fluorescence images of the transfected cells were taken. FRET was estimated by the acceptor photobleaching method. Protein–protein interaction was evaluated by FRET efficiency. RESULTS: The confocal fluorescence images showed that the cells expressing vimentin and R120G αB-crystallin contained large amounts of protein aggregates while few vimentin fibers were observed. FRET efficiency analyses indicated that vimentin had a significantly greater protein–protein interaction with R120G αB-crystallin than with WT αB-crystallin. CONCLUSIONS: Our results show that the R120G αB-crystallin mutant promoted vimentin aggregation through increased protein–protein interaction. This process may contribute to the formation of congenital cataract.