Tubulins in the primate retina: Evidence that xanthophylls may be endogenous ligands for the paclitaxel-binding site

The xanthophylls-lutein, zeaxanthin, and meso-zeaxanthin (L&Z)-are found in the central region of the primate retina, which is called the macula lutea (yellow spot). How they are anchored there and what their function is has been debated for over 50 years. Here, we present evidence that they may be bound to the paclitaxel (Taxol) binding site of the beta -tubulin subunit o f microtubules and that a major function may be to modulate the dynamic ins tability of microtubules in the macula. Also, we compare nucleic acid and a mino acid sequences of tubulins that are in human brain with those we have isolated from human-retina and monkey-macula cDNA libraries. In so doing, w e suggest that in primates, class I beta -tubulin consists of at least two subtypes (beta (Ia) and beta (Ib)). Alignment analysis of the sequences of the genes for beta (Ia) and beta (Ib) indicates that the corresponding mRNA s may have other functions in addition to that of coding for proteins. Furt hermore, we show that there are at least five different types of beta -tubu lin in the macula lutea of rhesus monkey. (C) 2001 Elsevier Science Ltd. Al l rights reserved.