Functional analysis of Photosystem I light-harvesting complexes (Lhca) gene products of Chlamydomonas reinhardtii |
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Authors: | Milena Mozzo Manuela Mantelli Francesca Passarini Stefano Caffarri Roberto Bassi |
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Institution: | a Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands b Univ Aix Marseille, Fac Sci Luminy, Lab Genet & Biophys Plantes, CEA, iBEB, SBVME, CNRS UMR Biologie Végétale et Microbiologie Environnementales, F-13009 Marseille, France c Dipartimento Scientifico e Tecnologico. Facoltà di Scienze MM.FF.NN. Università di Verona. Strada Le Grazie 15. 37134 Verona, Italy |
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Abstract: | The outer antenna system of Chlamydomonas reinhardtii Photosystem I is composed of nine gene products, but due to difficulty in purification their individual properties are not known. In this work, the functional properties of the nine Lhca antennas of Chlamydomonas, have been investigated upon expression of the apoproteins in bacteria and refolding in vitro of the pigment-protein complexes. It is shown that all Lhca complexes have a red-shifted fluorescence emission as compared to the antenna complexes of Photosystem II, similar to Lhca from higher plants, but less red-shifted. Three complexes, namely Lhca2, Lhca4 and Lhca9, exhibit emission maxima above 707 nm and all carry an asparagine as ligand for Chl 603. The comparison of the protein sequences and the biochemical/spectroscopic properties of the refolded Chlamydomonas complexes with those of the well-characterized Arabidopsis thaliana Lhcas shows that all the Chlamydomonas complexes have a chromophore organization similar to that of A. thaliana antennas, particularly to Lhca2, despite low sequence identity. All the major biochemical and spectroscopic properties of the Lhca complexes have been conserved through the evolution, including those involved in “red forms” absorption. It has been proposed that in Chlamydomonas PSI antenna size and polypeptide composition can be modulated in vivo depending on growth conditions, at variance as compared to higher plants. Thus, the different properties of the individual Lhca complexes can be functional to adapt the architecture of the PSI-LHCI supercomplex to different environmental conditions. |
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Keywords: | At Arabidopsis thaliana β-DM d-maltoside" target="_blank">n-dodecyl-β-d-maltoside Car carotenoid Chl chlorophyll Cr Chlamydomonas reinhardtii Lhca and LHCI light harvesting complex of PSI LHCII light-harvesting complex II PSI and PSII Photosystems I and II |
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