PROTEIN FOLDS AND FUNCTIONAL SIMILARITY - THE GREEK-KEY IMMUNOGLOBULIN FOLD

Investigations on a number of proteins in the Greek key/immunoglobulin superfold group using computer methods suggested that proteins contai ning modified Greek keys might exhibit some protein-protein interactio ns similar to those seen with immunoglobulins. The two domain beta-she et modified Greek key structure of the beta/gamma-crystallins is share d by other proteins, for example the chaperone protein PapD. Based on computer analysis, we tested for protein-protein interactions using pr otein A from Staphylococcus aureus, and showed that gamma-crystallin, unlike alpha- or gamma s-crystallins, exhibits weak protein A binding. beta-Crystallin exhibits much weaker binding than gamma-crystallin. P rotein A interaction may involve hydrophobic interactions around the i nterconnecting peptide region. We discuss the implications for the mol ecular evolution of the crystallins, the superfold, and for the molecu lar interactions in the mammalian lens that could be important in main taining transparency.