Rc. Bugos et al., XANTHOPHYLL CYCLE ENZYMES ARE MEMBERS OF THE LIPOCALIN FAMILY, THE FIRST IDENTIFIED FROM PLANTS, The Journal of biological chemistry, 273(25), 1998, pp. 15321-15324
Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the additi
on and removal of epoxide groups in carotenoids of the xanthophyll cyc
le in plants. The xanthophyll cycle is implicated in protecting the ph
otosynthetic apparatus from excessive light. Two new sequences for vio
laxanthin de-epoxidase from tobacco and Arabidopsis are described. Alt
hough the mature proteins are well conserved, the transit peptides of
these proteins are divergent, in contrast to transit peptides from oth
er proteins targeted to the thylakoid lumen. Sequence analyses of both
violaxanthin de-epoxidase and zeaxanthin epoxidase establish the xant
hophyll cycle enzymes as members of the lipocalin family of proteins.
The lipocalin family is a diverse group of proteins that bind small hy
drophobic (lipophilic) molecules and share a conserved tertiary struct
ure of eight P-strands forming a barrel configuration. This is the fir
st reported identification of lipocalin proteins in plants.