Spectroscopic studies on the interaction of calf lens membranes with crystallins

The interaction of crystallins with lens membranes and liposomes was studied by fluorescence and circular dichroism (CD) measurements. Two extrinsic fluorescence probes ANS (1-anilino-naphthalene-8-sulfonic acid) and DPH (1,6-diphenyl, 1,3,5-hexatriene) were used to detect the binding and to explore the binding site. The ANS fluorescence intensity is greater in membranes than in liposomes, but is reverse for DPH. Among alpha, beta and gamma-crystallins, only alpha c-crystallin decreased the ANS fluorescence intensity in membranes, indicating a binding between membranes and alpha c-crystallin. The binding site appears to be at the polar-apolar interface in membrane protein (MIP26) and alpha c-crystallin. Fluorescence polarization measurements show that lipid bilayer becomes less mobile with alpha c-crystallin binding. The change in the near UV CD due to the binding also indicates a decreased freedom of rotation of aromatic amino acid residues either in MIP26 or in alpha-crystallin.