title: A red-shifted antenna protein associated with photosystem II in Physcomitrella patens.
abstract: Antenna systems of plants and green algae are made up of pigment-protein complexes belonging to the light-harvesting complex (LHC) multigene family. LHCs increase the light-harvesting cross-section of photosystems I and II and catalyze photoprotective reactions that prevent light-induced damage in an oxygenic environment. The genome of the moss Physcomitrella patens contains two genes encoding LHCb9, a new antenna protein that bears an overall sequence similarity to photosystem II antenna proteins but carries a specific motif typical of photosystem I antenna proteins. This consists of the presence of an asparagine residue as a ligand for Chl 603 (A5) chromophore rather than a histidine, the common ligand in all other LHCbs. Asparagine as a Chl 603 (A5) ligand generates red-shifted spectral forms associated with photosystem I rather than with photosystem II, suggesting that in P. patens, the energy landscape of photosystem II might be different with respect to that of most green algae and plants. In this work, we show that the in vitro refolded LHCb9-pigment complexes carry a red-shifted fluorescence emission peak, different from all other known photosystem II antenna proteins. By using a specific antibody, we localized LHCb9 within PSII supercomplexes in the thylakoid membranes. This is the first report of red-shifted spectral forms in a PSII antenna system, suggesting that this biophysical feature might have a special role either in optimization of light use efficiency or in photoprotection in the specific environmental conditions experienced by this moss.
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada le Grazie 15, 37134 Verona, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Alboresi
authors.affiliation: Dipartimento di Biologia, Università di Padova, Via Ugo Bassi 58 B, 35121 Padova, Italy, and.
authors.forename: Caterina
authors.initials: C
authors.lastname: Gerotto
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada le Grazie 15, 37134 Verona, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Cazzaniga
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada le Grazie 15, 37134 Verona, Italy,; ICG-3, Phytosphäre Forschungszentrum Jülich, 52425 Jülich, Germany. Electronic address: roberto.bassi@univr.it.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.affiliation: Dipartimento di Biologia, Università di Padova, Via Ugo Bassi 58 B, 35121 Padova, Italy, and.
authors.forename: Tomas
authors.initials: T
authors.lastname: Morosinotto
mesh_terms: D019068:Bryopsida / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018745:Genome, Plant / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D010940:Plant Proteins