DOMAIN INTERACTIONS AND CONNECTING PEPTIDES IN LENS CRYSTALLINS

βB2- and γB-crystallin from bovine eye-lens are closely related proteins, topologically distinct mainly by virtue of the linker peptide connecting the two domains in each polypeptide chain. In homodimeric βB2-crystallin, the extended conformation of the connecting peptide has been suggested to force the βB2-molecule to favor intermolecular domain interactions compared with intramolecular contacts in monomeric γB-crystallin. From this one may postulate that the conserved interdomain contacts are essential for the overall stability of crystallins. This was clearly confirmed for γB-crystallin, since its isolated C-terminal domain is significantly less stable than in the context of native γB. Exchanging the linker peptide of γB- for that of βB2-crystallin yields a monomeric protein with stability characteristics identical to γB-crystallin. We conclude that the domain-interface itself rather than the connecting peptide determines the mode of domain association in crystallins, as the linker in the γBβ-mutant is evidently twisted to a turn similar to the one in natural γB-crystallin. © 1994 Academic Press Limited.