title: The Antarctic Psychrophile Chlamydomonas sp. UWO 241 Preferentially Phosphorylates a Photosystem I-Cytochrome b6/f Supercomplex.
abstract: Chlamydomonas sp. UWO 241 (UWO 241) is a psychrophilic green alga isolated from Antarctica. A unique characteristic of this algal strain is its inability to undergo state transitions coupled with the absence of photosystem II (PSII) light-harvesting complex protein phosphorylation. We show that UWO 241 preferentially phosphorylates specific polypeptides associated with an approximately 1,000-kD pigment-protein supercomplex that contains components of both photosystem I (PSI) and the cytochrome b₆/f (Cyt b₆/f) complex. Liquid chromatography nano-tandem mass spectrometry was used to identify three major phosphorylated proteins associated with this PSI-Cyt b₆/f supercomplex, two 17-kD PSII subunit P-like proteins and a 70-kD ATP-dependent zinc metalloprotease, FtsH. The PSII subunit P-like protein sequence exhibited 70.6% similarity to the authentic PSII subunit P protein associated with the oxygen-evolving complex of PSII in Chlamydomonas reinhardtii. Tyrosine-146 was identified as a unique phosphorylation site on the UWO 241 PSII subunit P-like polypeptide. Assessment of PSI cyclic electron transport by in vivo P700 photooxidation and the dark relaxation kinetics of P700(+) indicated that UWO 241 exhibited PSI cyclic electron transport rates that were 3 times faster and more sensitive to antimycin A than the mesophile control, Chlamydomonas raudensis SAG 49.72. The stability of the PSI-Cyt b₆/f supercomplex was dependent upon the phosphorylation status of the PsbP-like protein and the zinc metalloprotease FtsH as well as the presence of high salt. We suggest that adaptation of UWO 241 to its unique low-temperature and high-salt environment favors the phosphorylation of a PSI-Cyt b₆/f supercomplex to regulate PSI cyclic electron transport rather than the regulation of state transitions through the phosphorylation of PSII light-harvesting complex proteins.
authors.affiliation: Biology Department and Biotron Centre for Experimental Climate Change Research, University of Western Ontario, London, Ontario, Canada N6A 5B7 (B.S.-M., A.G.I., N.P.A.H.); andDepartment of Biochemistry and Biological Mass Spectrometry Laboratory, University of Western Ontario, London, Ontario, Canada N6G 2V4 (P.P., G.L.).
authors.forename: Beth
authors.initials: B
authors.lastname: Szyszka-Mroz
authors.affiliation: Biology Department and Biotron Centre for Experimental Climate Change Research, University of Western Ontario, London, Ontario, Canada N6A 5B7 (B.S.-M., A.G.I., N.P.A.H.); andDepartment of Biochemistry and Biological Mass Spectrometry Laboratory, University of Western Ontario, London, Ontario, Canada N6G 2V4 (P.P., G.L.).
authors.forename: Paula
authors.identifier: http://orcid.org/0000-0003-0597-419X
authors.initials: P
authors.lastname: Pittock
authors.affiliation: Biology Department and Biotron Centre for Experimental Climate Change Research, University of Western Ontario, London, Ontario, Canada N6A 5B7 (B.S.-M., A.G.I., N.P.A.H.); andDepartment of Biochemistry and Biological Mass Spectrometry Laboratory, University of Western Ontario, London, Ontario, Canada N6G 2V4 (P.P., G.L.).
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Ivanov
authors.affiliation: Biology Department and Biotron Centre for Experimental Climate Change Research, University of Western Ontario, London, Ontario, Canada N6A 5B7 (B.S.-M., A.G.I., N.P.A.H.); andDepartment of Biochemistry and Biological Mass Spectrometry Laboratory, University of Western Ontario, London, Ontario, Canada N6G 2V4 (P.P., G.L.).
authors.forename: Gilles
authors.initials: G
authors.lastname: Lajoie
authors.affiliation: Biology Department and Biotron Centre for Experimental Climate Change Research, University of Western Ontario, London, Ontario, Canada N6A 5B7 (B.S.-M., A.G.I., N.P.A.H.); andDepartment of Biochemistry and Biological Mass Spectrometry Laboratory, University of Western Ontario, London, Ontario, Canada N6G 2V4 (P.P., G.L.) nhuner@uwo.ca.
authors.forename: Norman P A
authors.identifier: http://orcid.org/0000-0001-8723-6961
authors.initials: NP
authors.lastname: Hüner
mesh_terms: D000595:Amino Acid Sequence; D000968:Antimycin A / Q000494:pharmacology; D005591:Chemical Fractionation; D002696:Chlamydomonas / Q000187:drug effects / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D045346:Cytochrome b6f Complex / Q000378:metabolism*; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects; D015180:Electrophoresis, Gel, Two-Dimensional; D015151:Immunoblotting; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D055550:Protein Stability / Q000187:drug effects; D016415:Sequence Alignment; D012965:Sodium Chloride / Q000494:pharmacology; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism
chemical_list: D046912:Multiprotein Complexes; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; D012965:Sodium Chloride; C037184:chlorophyll b; D000968:Antimycin A; D045346:Cytochrome b6f Complex; D004237:Diuron; D000077194:Chlorophyll A