Prediction of stability factors at the domain interface of human gammaB crystallin maintaining the transparency of the eye lens.

Objective: βγ-crystallins are among the most long lived globular proteins known today. Interaction of the two domains through a hydrophobic interface is one of the major contributors to the stability of these crystallins.Changes in these interactions are either due to the amino acid substitutions or the changes in the orientations of the same amino acids leading to cataract formation. We have carried out a detailed analysis to observe the stabilizing effects of hydrophobic core residues at the domain interface of the predicted human γB-aystallin structure. Methods: Human yB-crystallin model was built by Homology Modeling hsing MODELLER4 based on the crystal structure coordinates of bovine yB-crystallin. In lens yB-crystallin, there are six non polar residues, three each in the two domains which form a hydrophobic core at the domain interface. We performed mutational studies at position 56 and analyzed the changes in the protein structure. Three mutants (Phe→Trp. Phe→Ala, Phe→Asp) were constructed and analyzed for hydrogen bonding, ion pairs and accessibility by WHATIF web server. Results: Being the largest amino acid among the six residues taking part in the hydrophobic interactions at the domain interface, Phe was predicted to be responsible for the greatest contribution to the stability at this region. Phe→Ala mutant showed the largest structural changes in the vicinity of the mutated residue. Conclusion: The results obtained clearly emphasize the importance of hydrophobic interactions to the stability of crystallins. Mutations at the domain interphase could decrease the interactions between these domains thus causing destability.