期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1999
卷号：96
期号：18
页码：10056-10061
DOI：10.1073/pnas.96.18.10056
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The chromophore-binding properties of the higher plant light-harvesting protein CP29 have been studied by using site-directed mutagenesis of pigment-binding residues. Overexpression of the apoproteins in bacteria was followed by reconstitution in vitro with purified pigments, thus obtaining a family of mutant CP29 proteins lacking individual chromophore-binding sites. Biochemical characterization allowed identification of the eight porphyrins and two xanthophyll-binding sites. It is shown that the four porphyrin-binding sites (A1, A2, A4, and A5) situated in the central, twofold-symmetrical domain of the protein are selective for Chl-a, whereas the four peripheral sites (A3, B3, B5, and B6) have mixed Chl-a-Chl-b specificity. Within a site, porphyrin coordination by glutamine increases affinity for Chl-b as compared with glutamate. Xanthophyll site L1 is occupied by lutein, whereas site L2 can bind violaxanthin or neoxanthin. The protein is relatively stable when site L2 site is empty, suggesting that xanthophylls can be exchanged during operation of xanthophyll cycle-dependent photoprotection mechanism. Differential absorption spectroscopy allowed determination of transition energy levels for individual chromophores, thus opening the way to calculation of energy-transfer rates between Chl in higher plant antenna proteins.
关键词：photosynthesis ; chlorophyll ; protein folding ; CP29
