VITAMIN-A(2) BOUND TO CELLULAR RETINOL-BINDING PROTEIN AS ULTRAVIOLETFILTER IN THE EYE LENS OF THE GECKO LYGODACTYLUS-PICTURATUS

The yellow eye lenses of the diurnal gecko Lygodactylus picturatus con tain, in addition to the usual crystallins, a monomeric protein with a molecular mass of 16 kDa., It comprises 6-8% of the total water-solub le lens proteins. We here identify it as a novel type of crystallin, m ost closely related with cellular retinol-binding protein I (CRBP I), Because of its tiny size, we designate it as L-crystallin. The typical endogenous ligand of CRBP is all-trans-retinol. In the gecko lens, ho wever, the ligand of L-crystallin turns out to be 3-dehydroretinol (vi tamin A(2)), which causes the yellow color of this lens, The L-crystal lin . 3-dehydroretinol complex absorbs shortwave radiation, supposedly improving the optical quality of the dioptric apparatus and protectin g the retina against ultraviolet damage, Whereas other crystallins hav e been recruited from stress proteins and metabolic enzymes, L-crystal lin represents a completely new class of taxon-specific lens proteins, Also, its ligand 3-dehydroretinol represents a novel type of lens pig ment.