Localization of the N-terminal domain in light-harvesting chlorophyll a/b protein by EPR measurements.
The conformational distribution of the N-terminal domain of the major light-harvesting chlorophyll a/b protein (LHCIIb) has been characterized by electron-electron double resonance yielding distances between spin labels placed in various domains of the protein. Distance distributions involving residue 3 near the N terminus turned out to be bimodal, revealing that this domain, which is involved in regulatory functions such as balancing the energy flow through photosystems (PS) I and II, exists in at least two conformational states. Models of the conformational sub-ensembles were generated on the basis of experimental distance restraints from measurements on LHCIIb monomers and then checked for consistency with the experimental distance distribution between residues 3 in trimers. Only models where residue 3 is located above the core of the protein and extends into the aqueous phase on the stromal side fit the trimer data. In the other state, which consequently is populated only in monomers, the N-terminal domain extends sideways from the protein core. The two conformational states may correspond to two functional states of LHCIIb, namely trimeric LHCIIb associated with PSII in stacked thylakoid membranes and presumably monomeric LHCIIb associated with PSI in nonstacked thylakoids. The switch between these two is known to be triggered by phosphorylation of Thr-6. A similar phosphorylation-induced conformational change of the N-terminal domain has been observed by others in bovine annexin IV which, due to the conformational switch, also loses its membrane-aggregating property.
Jeschke
Gunnar
G
Max-Planck-Institut für Polymerforschung, Postfach 3148, 55021 Mainz, Germany.
Bender
Alexander
A
Schweikardt
Thorsten
T
Panek
Grazyna
G
Decker
Heinz
H
Paulsen
Harald
H
D000818:Animals; D017314:Annexin A4 / Q000737:chemistry; D002417:Cattle; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D018360:Crystallography, X-Ray; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D004926:Escherichia coli / Q000378:metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances / Q000737:chemistry; D008958:Models, Molecular; D009154:Mutation; D010100:Oxygen / Q000737:chemistry; D018532:Pisum sativum / Q000378:metabolism; D010766:Phosphorylation; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D013113:Spin Labels; D013912:Threonine / Q000737:chemistry; D020524:Thylakoids / Q000378:metabolism; D013997:Time Factors
D017314:Annexin A4; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins; D013113:Spin Labels; D002734:Chlorophyll; D013912:Threonine; C037184:chlorophyll b; D010100:Oxygen; D000077194:Chlorophyll A