Confocal fluorescence resonance energy transfer microscopy study of protein-protein interactions of lens crystallins in living cells

PURPOSE: To determine protein-protein interactions among lens crystallins in living cells. METHODS: Fluorescence resonance energy transfer (FRET) microscopy was used to visualize interactions in living cells directly. Two genes, one (αA-crystallin) fused with green fluorescence protein (GFP) and the other (each of the following genes: αB-, βB2-, γC-crystallin, and R120G αB-crystallin mutant) fused with GFP variant red fluorescence protein (RED), were cotransfected into HeLa cells. After culture, confocal microscopy images were taken and FRET values were calculated. RESULTS: FRET occurs when the two proteins interact. The data show strong interactions between αA- and αB-crystallin and weak interactions between αA- and βB2- or γC-crystallin, which is consistent with our previous two-hybrid system study. The R120G αB-crystallin mutant, however, showed significantly less FRET than wild-type αB-crystallin. There are also more R120G αB-crystallin transfected cells with protein aggregates than wild-type αB-crystallin transfected cells. Cotransfection with αA-crystallin could not rescue R120G αB-crystallin from aggregation. CONCLUSIONS: FRET microscopy gave excellent results on the protein-protein interactions among crystallins. It supports many previous studies and provides a novel technique for further study of protein-protein interactions among lens proteins including membrane and cytoskeletal proteins.