title: Stoichiometry of LHCI antenna polypeptides and characterization of gap and linker pigments in higher plants Photosystem I.
abstract: We report on the results obtained by measuring the stoichiometry of antenna polypeptides in Photosystem I (PSI) from Arabidopsis thaliana. This analysis was performed by quantification of Coomassie blue binding to individual LHCI polypeptides, fractionation by SDS/PAGE, and by the use of recombinant light harvesting complex of Photosystem I (Lhca) holoproteins as a standard reference. Our results show that a single copy of each Lhca1-4 polypeptide is present in Photosystem I. This is in agreement with the recent structural data on PSI-LHCI complex [Ben Shem, A., Frolow, F. and Nelson, N. (2003) Nature, 426, 630-635]. The discrepancy from earlier estimations based on pigment binding and yielding two copies of each LHCI polypeptide per PSI, is explained by the presence of 'gap' and 'linker' chlorophylls bound at the interface between PSI core and LHCI. We showed that these chlorophylls are lost when LHCI is detached from the PSI core moiety by detergent treatment and that gap and linker chlorophylls are both Chl a and Chl b. Carotenoid molecules are also found at this interface between LHCI and PSI core. Similar experiments, performed on PSII supercomplexes, showed that dissociation into individual pigment-proteins did not produce a significant loss of pigments, suggesting that gap and linker chlorophylls are a peculiar feature of Photosystem I.
authors.affiliation: Dipartimento Scientifico e Tecnologico, Università di Verona, Verona, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Ballottari
authors.forename: Chiara
authors.initials: C
authors.lastname: Govoni
authors.forename: Stefano
authors.initials: S
authors.lastname: Caffarri
authors.forename: Tomas
authors.initials: T
authors.lastname: Morosinotto
mesh_terms: D017360:Arabidopsis / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D010860:Pigments, Biological / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*
chemical_list: D045331:Photosystem I Protein Complex; D010860:Pigments, Biological; D010940:Plant Proteins; D002734:Chlorophyll; D002338:Carotenoids