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A recent study demonstrated the presence of protein-protein interactions among lens crystallins in a mammalian cell two-hybrid system assay and speculated about the significance of these interactions for protein solubility and lens transparency. The current study extends those findings to the following crystallin genes involved in some congenital cataracts: CRYAA (R116C), CRYAB (R120G), and CRYGC (T5P).
A mammalian two-hybrid system was used to assay the protein-protein interactions. Congenital cataract crystallin genes were cloned and fused into the two-hybrid system vectors (target and prey proteins). Together, with the third vector containing a reporter gene, chloramphenicol acetyltransferase (CAT), they were cotransfected into human HeLa cells. The presence of protein-protein interactions and the strength of these interactions were assayed by CAT ELISA.
The pattern of changes in protein-protein interactions of those congenital cataract gene products with the three major crystallins, alphaA- or alphaB-, betaB2-, and gammaC-crystallins, differed. For the T5P gammaC-crystallin, most of the interactions were decreased; for the R116C alphaA-crystallin, the interactions with betaB2- and gammaC-crystallin decreased and those with alphaB-crystallin and heat-shock protein (Hsp)27 increased; and for the R120G alphaB-crystallin, the interactions with alphaA- and alphaB-crystallin decreased, but those with betaB2- and gammaC-crystallin increased slightly. An attempt was made to interpret the results on the basis of conformational change and disruption of dimeric interaction involving beta-strands.
The results clearly indicate that crystallin mutations involved in congenital cataracts altered protein-protein interactions, which may contribute to decreased protein solubility and formation of cataract.