title: Posttranslational modifications in the CP43 subunit of photosystem II.
abstract: Photosystem II (PSII) catalyzes the light-driven oxidation of water and the reduction of plastoquinone; the oxidation of water occurs at a cluster of four manganese. The PSII CP43 subunit functions in light harvesting, and mutations in the fifth luminal loop (E) of CP43 have established its importance in PSII structure and/or assembly [Kuhn, M. G. & Vermaas, V. F. J. (1993) Plant Mol. Biol. 23, 123-133]. The sequence A(350)PWLEPLR(357) in luminal loop E is conserved in CP43 genes from 50 organisms. To map important posttranslational modifications in this sequence, tandem mass spectrometry (MS/MS) was used. These data show that the indole side chain of Trp-352 is posttranslationally modified to give mass shifts of +4, +16, and +18 daltons. The masses of the modifications suggest that the tryptophan is modified to kynurenine (+4), a keto-/amino-/hydroxy- (+16) derivative, and a dihydro-hydroxy- (+18) derivative of the indole side chain. Peptide synthesis and MS/MS confirmed the kynurenine assignment. The +16 and +18 tryptophan modifications may be intermediates formed during the oxidative cleavage of the indole ring to give kynurenine. The site-directed mutations, W352C, W352L, and W352A, exhibit an increased rate of photoinhibition relative to wild type. We hypothesize that Trp-352 oxidative modifications are a byproduct of PSII water-splitting or electron transfer reactions and that these modifications target PSII for turnover. As a step toward understanding the tertiary structure of this CP43 peptide, structural modeling was performed by using molecular dynamics.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, St. Paul 55108, USA.
authors.forename: Lorraine B
authors.initials: LB
authors.lastname: Anderson
authors.forename: Melissa
authors.initials: M
authors.lastname: Maderia
authors.forename: Anthony J A
authors.initials: AJ
authors.lastname: Ouellette
authors.forename: Cindy
authors.initials: C
authors.lastname: Putnam-Evans
authors.forename: LeeAnn
authors.initials: L
authors.lastname: Higgins
authors.forename: Thomas
authors.initials: T
authors.lastname: Krick
authors.forename: Michael J
authors.initials: MJ
authors.lastname: MacCoss
authors.forename: Hanjo
authors.initials: H
authors.lastname: Lim
authors.forename: John R
authors.initials: JR
authors.lastname: Yates
authors.forename: Bridgette A
authors.initials: BA
authors.lastname: Barry
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D002734:Chlorophyll / Q000378:metabolism; D016384:Consensus Sequence; D045342:Light-Harvesting Protein Complexes; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010100:Oxygen / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D010449:Peptide Mapping; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D002734:Chlorophyll; D010100:Oxygen