title: Protein-protein interactions by molecular modeling and biochemical characterization of PSI-LHCI supercomplexes from Chlamydomonas reinhardtii.
abstract: The physiological function of Photosystem I (PSI) is a sunlight energy converter, catalyzing one of the initial steps in driving oxygenic photosynthesis in cyanobacteria, algae and higher plants. The Chlamydomonas reinhardtii PSI structure was not known since it contains a unique structure having additional light harvesting complex I (LHCI) subunits, which play a major role in the transfer of sunlight energy to the reaction center. Here, individual subunits of LHC and core subunits are built based on the PDB taken from RCSB Protein Data Bank. The model gives information about the geometrical existence of subunits following a flanking order of Lhca5, Lhca1, Lhca6, Lhca4, Lhca2, Lhca8, Lhca9, Lhca7, and Lhca3. The new subunit PsaO is located close to the PsaH, PsaI and PsaL subunits, thus it may be involved in the state transition mechanism and stabilization of PSI-LHCI supercomplexes. The modeled PSI-LHCI structure of C. reinhardtii shows a unique arrangement of PsaN, PsaO of PSI core subunits and Lhca5 to Lhca9 of LHCI subunits. There are many non-covalent interactions among the PSI and LHCI subunits, which suggest that C. reinhardtii PSI-LHCI supercomplexes are more complex than higher plants. These results strongly support the experimental data that, even with harsh treatment of the PSI-LHCI supercomplexes with detergent, the complexes do not dissociate due to strong interactions between the PSI core and LHCI. Thus, our 3D model may give valid structural information of the PSI-LHCI arrangement and its physiological role in C. reinhardtii.
authors.affiliation: Department of Biochemistry, University of Hyderabad, Hyderabad, India 500046.
authors.forename: Venkateswarlu
authors.initials: V
authors.lastname: Yadavalli
authors.forename: Chandramouli
authors.initials: C
authors.lastname: Malleda
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Subramanyam
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D030562:Databases, Protein; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D060066:Protein Interaction Maps; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D055672:Static Electricity
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D021122:Protein Subunits