EYE LENS TRANSPARENCY OR COLD CATARACT : A QUESTION OF PROTEIN INTERACTION POTENTIALS. Annette Tardieu¹, Marc Malfois¹, Françoise Bonneté¹ & Luc Belloni². ¹Laboratoire de Minéralogie Cristallographie, Tour 16, Case 115, 4 Place Jussieu, F-75252 Paris Cedex 05, France; ²CEA-DRECAM, Service de Chimie Moléculaire, Centre d'Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, France

Interaction potentials between the eye lens proteins, the crystallins, account for eye lens optical properties. Alpha-crystallin repulsive interactions control lens transparency whereas gamma-crystallin attractive interactions are responsible for a fluid-fluid phase separation with decreasing temperature, known as cold cataract.

Small angle X-ray scattering was used to construct crystallin phase diagrams. Experimental structure factors were measured in a variety of physico-chemical conditions : pH, ionic strengh and temperature. Theoretical structure factors, calculated using the numerical methods developped in liquid state and colloÏd physics, allowed us to determine the best fit parameters of the attractive and repulsive potentials. Relationships with macromolecular properties could be inferred. The protein charge generates a coulombic repulsive potential that is a function of pH and Debye length. The attractive Van der Waals forces are sufficient to account for the gamma-crystallin phase separation. Entropic effects, however, contribute to the attractive potentials at high ionic strengh.