Structural characterization of a complex of photosystem I and light-harvesting complex II of Arabidopsis thaliana.
Chloroplasts are central to the provision of energy for green plants. Their photosynthetic membrane consists of two major complexes converting sunlight: photosystem I (PSI) and photosystem II (PSII). The energy flow toward both photosystems is regulated by light-harvesting complex II (LHCII), which after phosphorylation can move from PSII to PSI in the so-called state 1 to state 2 transition and can move back to PSII after dephosphorylation. To investigate the changes of PSI and PSII during state transitions, we studied the structures and frequencies of all major membrane complexes from Arabidopsis thaliana chloroplasts at conditions favoring either state 1 or state 2. We solubilized thylakoid membranes with digitonin and analyzed the complete set of complexes immediately after solubilization by electron microscopy and image analysis. Classification indicated the presence of a PSI-LHCII supercomplex consisting of one PSI-LHCI complex and one LHCII trimer, which was more abundant in state 2 conditions. The presence of LHCII was confirmed by excitation spectra of the PSI emission of membranes in state 1 or state 2. The PSI-LHCII complex could be averaged with a resolution of 16 A, showing that LHCII has a specific binding site at the PSI-A, -H, -L, and -K subunits.
Kouril
Roman
R
Department of Biophysical Chemistry, GBB, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Zygadlo
Agnieszka
A
Arteni
Ana A
AA
de Wit
Chantal D
CD
Dekker
Jan P
JP
Jensen
Poul Erik
PE
Scheller
Henrik Vibe
HV
Boekema
Egbert J
EJ
D017360:Arabidopsis / Q000737:chemistry* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D017348:Microscopy, Electron, Scanning Transmission; D045331:Photosystem I Protein Complex / Q000145:classification / Q000378:metabolism / Q000648:ultrastructure*; D018515:Plant Leaves / Q000737:chemistry* / Q000378:metabolism; D020836:Protein Structure, Quaternary; D020524:Thylakoids / Q000737:chemistry* / Q000502:physiology
D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex