Mutational analysis of a higher plant antenna protein provides identification of chromophores bound into multiple sites

Roberto Bassi*, Roberta Croce, Daniela Cugini, Dorianna Sandonà

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

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 AS) 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.

Original languageEnglish
Pages (from-to)10056-10061
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume96
Issue number18
DOIs
Publication statusPublished - 31 Aug 1999

Keywords

  • Chlorophyll
  • CP29
  • Photosynthesis
  • Protein folding

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