ALPHA-CRYSTALLIN QUATERNARY STRUCTURE AND INTERACTIVE PROPERTIES CONTROL EYE LENS TRANSPARENCY

The eye lens is the foremost biological system where function is direc tly under control of the physico-chemical properties of the cytoplasmi c macromolecular solution. Indeed, lens transparency and opacity, lens refractive index gradient and viscosity, are the result of the struct ural and interactive properties of the crystallins, of their stability , of the fine tuning of their interaction potentials and associations at different levels of organization. Among the different crystallin cl asses, alpha-crystallins have represented a major challenge for a long time. The alpha-crystallin secondary, tertiary and quaternary structu res are still unknown. On the functional side, however, it is establis hed that alpha-crystallin quaternary structure and repulsive interacti ons determine lens transparency, whereas the alpha-crystallin chaperon e effect most probably plays a role in the aging process. In the prese nt paper, we recall the physico-chemical properties and the quaternary structure features of alpha-crystallins that were demonstrated to con trol light scattering and transparency. The interest of a crystallin m ixture for lens function is discussed. Then, a formal approach is prop osed to design models for the alpha-crystallin quaternary structure, i ncluding the question of whether alpha-crystallins assemble with symme try. An hypothesis relevant to the fold of the alpha-crystallin C-term inal domain is presented in another paper in this issue. (C) 1998 Else vier Science B.V. All rights reserved.