| First Author | Werten PJ | Year | 2000 |
| Journal | Proc Natl Acad Sci U S A | Volume | 97 |
| Issue | 7 | Pages | 3282-7 |
| PubMed ID | 10725366 | Mgi Jnum | J:61374 |
| Mgi Id | MGI:1354842 | Doi | 10.1073/pnas.050500597 |
| Citation | Werten PJ, et al. (2000) Gecko iota-crystallin: how cellular retinol-binding protein became an eye lens ultraviolet filter. Proc Natl Acad Sci U S A 97(7):3282-7 |
| abstractText | Eye lenses of various diurnal geckos contain up to 12% iota-crystallin. This protein is related to cellular retinol-binding protein type I (CRBP I) but has 3,4-didehydroretinol, rather than retinol, as a ligand. The 3,4-didehydroretinol gives the lens a yellow color, thus protecting the retina by absorbing short-wave radiation. iota-Crystallin could be either the gecko's housekeeping CRBP I, recruited for an additional function in the lens, or the specialized product of a duplicated CRBP I gene. The finding of the same CRBP I-like sequence in lens and liver cDNA of the gecko Lygodactylus picturatus now supports the former option. Comparison with iota-crystallin of a distantly related gecko, Gonatodes vittatus, and with mammalian CRBP I, suggests that acquiring the additional lens function is associated with increased amino acid changes. Compared with the rat CRBP I structure, the iota-crystallin model shows reduced negative surface charge, which might facilitate the required tight protein packing in the lens. Other changes may provide increased stability, advantageous for a long-living lens protein, without frustrating its role as retinol transporter outside the lens. Despite a number of replacements in the ligand pocket, recombinant iota-crystallin binds 3,4-didehydroretinol and retinol with similar and high affinity (approximately 1.6 nM). Availability of ligand thus determines whether it binds 3,4-didehydroretinol, as in the lens, or retinol, in other tissues. iota-Crystallin presents a striking example of exploiting the potential of an existing gene without prior duplication. |
