Characterization of a novel Photosystem I–LHCI supercomplex isolated from Chlamydomonas reinhardtii under anaerobic (State II) conditions

• Published in: FEBS letters 2006-01, Vol.580 (1), p.233-238
• Main Authors: Subramanyam, Rajagopal, Jolley, Craig, Brune, Daniel C., Fromme, Petra, Webber, Andrew N.
• Format: Article
• Language: English
• Subjects: Acclimatization - physiology; Algal Proteins - chemistry; Algal Proteins - isolation & purification; Algal Proteins - metabolism; Anaerobic; Anaerobiosis - physiology; Animals; Binding Sites; Chl; Chlamydomonas; Chlamydomonas reinhardtii; Chlamydomonas reinhardtii - enzymology; Chlamydomonas reinhardtii - growth & development; chlorophyll; Chlorophyll - chemistry; Chlorophyll - isolation & purification; Chlorophyll - metabolism; circular dichroism; Energy Transfer - physiology; FDAS; fluorescence decay associated spectra; Freshwater; Kinetics; LHC; light harvesting complex; Light-Harvesting Protein Complexes - chemistry; Light-Harvesting Protein Complexes - isolation & purification; Light-Harvesting Protein Complexes - metabolism; MALDI-TOF; matrix-assisted laser desorption ionization-time-of-flight mass spectrometry; optical density; Oxidation-Reduction; photosystem; Photosystem I Protein Complex - chemistry; Photosystem I Protein Complex - isolation & purification; Photosystem I Protein Complex - metabolism; plastoquinone; PQ oxidized; PQ reduced; PSI–LHCI Supercomplex; SDS–PAGE; single photon counting; sodium dodecyl sulfate–polyacrylamide gel electrophoresis; SPC; Spectrometry, Fluorescence; State; State I and II; State transitions
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/j.febslet.2005.12.003

A novel supercomplex of Photosystem I (PSI) with light harvesting complex I (LHCI) was isolated from the green alga Chlamydomonas reinhardtii. This novel supercomplex is unique as it is the first stable supercomplex of PSI together with its external antenna. The supercomplex contains 256 chlorophylls per reaction center. The supercomplex was isolated under anaerobic conditions and may represent the State II form of the photosynthetic unit. In contrast to previously reported supercomplexes isolated in State I, which contain only 4 LHC I proteins, this supercomplex contains 10–11 LHC I proteins tightly bound to the PSI core. In contrast to plants, no LHC II is tightly bound to the PSI–LHCI supercomplex in State II. Investigation of the energy transfer from the antenna system to the reaction center core shows that the LHC supercomplexes are tightly coupled to the PSI core, not only structurally but also energetically. The excitation energy transfer kinetics are completely dominated by the fast phase, with a near-complete lack of long-lived fluorescence. This tight coupling is in contrast to all reports of energy transfer in PSI–LHCI supercomplexes (in State I), which have so far been described as weakly coupled supercomplexes with low efficiency for excitation energy transfer. These results indicate that there are large and dynamic changes of the PSI–LHCI supercomplex during the acclimation from aerobic (State I) to anaerobic (State II) conditions in Chlamydomonas.