tailieunhanh - Báo cáo khoa học: Light-harvesting complex II protein CP29 binds to photosystem I of Chlamydomonas reinhardtii under State 2 conditions

The State 1 to State 2 transition in the photosynthetic membranes of plants and green algae involves the functional coupling of phosphorylated light-harvesting complexes of photosystem II (LHCII) to photosystem I (PSI). We present evidence suggesting that inChlamydomonas reinhardtiithis coupling may be aided by a hyper-phosphorylated form of the LHCII-like CP29 protein (Lhcbm4). | ềFEBS Journal Light-harvesting complex II protein CP29 binds to photosystem I of Chlamydomonas reinhardtii under State 2 conditions Joanna Kargul1 Maria V. Turkina2 Jon Nield1 Sam Benson1 Alexander V. Vener2 and James Barber1 1 Wolfson Laboratories Division of Molecular Biosciences Imperial college London UK 2 Division of Cell Biology Linkoping University Sweden Keywords Chlamydomonas CP29 photosynthesis protein phosphorylation State transitions Correspondence J. Barber Division of Molecular Biosciences Imperial college London South Kensington Campus London SW7 2AZ UK Fax 44 20 7594 5267 Tel 44 20 7594 5266 E-mail Received 17 June 2005 revised 29 July 2005 accepted 2 August 2005 doi The State 1 to State 2 transition in the photosynthetic membranes of plants and green algae involves the functional coupling of phosphorylated lightharvesting complexes of photosystem II LHCII to photosystem I PSI . We present evidence suggesting that in Chlamydomonas reinhardtii this coupling may be aided by a hyper-phosphorylated form of the LHCII-like CP29 protein Lhcbm4 . MS analysis of CP29 showed that Thr6 Thr16 and Thr32 and Ser102 are phosphorylated in State 2 whereas in State 1-exposed cells only phosphorylation of Thr6 and Thr32 could be detected. The LHCI-PSI supercomplex isolated from the alga in State 2 was found to contain strongly associated CP29 in phosphorylated form. Electron microscopy suggests that the binding site for this highly phosphorylated CP29 is close to the PsaH protein. It is therefore postulated that redoxdependent multiple phosphorylation of CP29 in green algae is an integral part of the State transition process in which the structural changes of CP29 induced by reversible phosphorylation determine the affinity of LHCII for either of the two photosystems. Excitation of the membrane-bound protein complexes photosystem I PSI and II PSII by light must be optimized to ensure the highest efficiency of .

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