Nearest-neighbor analysis of higher-plant photosystem I holocomplex.
Photosystem 1 (PSI) preparations from barley (Hordeum vulgare) and spinach (Spinacia oleracea) were subjected to chemical cross-linking using the cleavable homobifunctional cross-linkers dithiobis(succinimidylpropionate) and 3,3'-dithiobis(sulfosuccinimidyl-propionate). The overall pattern of cross-linked products was analyzed by the simple but powerful technique of diagonal electrophoresis, in which the disulfide bond in the cross-linker was cleaved between the first and second dimensions of the gel, and immunoblotting. A large number of cross-linked products were identified. Together with preexisting data on the structure of PSI, it was deduced that the subunits PSI-D, PSI-H, PSI-I, and PSI-L occupy one side of the complex, whereas PSI-E, PSI-F, and PSI-J occupy the other. PSI-K and PSI-G appear to be adjacent to Lhca3 and Lhca2, respectively, and not close to the other small subunits. Experiments with isolated light-harvesting complex I preparations indicate that the subunits are organized as dimers, which seem to associate to the PSI-A/PSI-B proteins independent of each other. We suggest which PSI subunit corresponds to each membrane-spanning helix in the cyanobacterial PSI structure, and present a model for higher-plant PSI.
Jansson
S
S
Department of Plant Biology, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark. stefan.jansson@plantphys.umu.se
Andersen
B
B
Scheller
H V
HV
D000595:Amino Acid Sequence; D000906:Antibodies; D003432:Cross-Linking Reagents; D019281:Dimerization; D000939:Epitopes / Q000032:analysis; D001467:Hordeum / Q000378:metabolism*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification; D045331:Photosystem I Protein Complex; D018724:Spinacia oleracea / Q000378:metabolism*
D000906:Antibodies; D003432:Cross-Linking Reagents; D000939:Epitopes; D046911:Macromolecular Substances; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex