title: Structural and functional changes of PSI-LHCI  supercomplexes of Chlamydomonas reinhardtii cells  grown under high salt conditions.
abstract: The eVect of high salt concentration (100 mM NaCl) on the organization of photosystem I-light harvesting complex I supercomplexes (PSI-LHCI) of Chlamydomonas reinhardtii was studied. The electron transfer activity was reduced by 39% in isolated PSI-LHCI supercomplexes. The visible circular dichroism (CD) spectra associated with strongly coupled chlorophyll (Chl) dimers were reduced in intensity, indicating that pigment-pigment interactions were disrupted. This data is consistent with results from Xuorescence streak camera spectroscopy, which suggest that red-shifted pigments in the PSI-LHCI antenna had been lost. Denaturing gel electrophoresis and immunoblot analysis reveals that levels of the PSI reaction center proteins PsaD, PsaE and PsaF were reduced due to salt stress. PsaE is almost completely absent under high salt conditions. It is known that the membrane-extrinsic subunits PsaD and E form the ferredoxin-docking site. Our results indicate that the PSI-LHCI supercomplex is damaged by reactive oxygen species at high salt concentration, with particular impact on the ferredoxin-docking site and the PSILHCI interface.
authors.affiliation: Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad 500046, India. srgsl@uohyd.ernet.in
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Subramanyam
authors.forename: Craig
authors.initials: C
authors.lastname: Jolley
authors.forename: Balakumar
authors.initials: B
authors.lastname: Thangaraj
authors.forename: Sreedhar
authors.initials: S
authors.lastname: Nellaepalli
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Webber
authors.forename: Petra
authors.initials: P
authors.lastname: Fromme
mesh_terms: D020418:Algal Proteins / Q000737:chemistry* / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000378:metabolism*; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D010100:Oxygen / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D045331:Photosystem I Protein Complex; D012965:Sodium Chloride; D013482:Superoxide Dismutase; D010100:Oxygen