Posttranslational modifications in the CP43 subunit of photosystem II

Lorraine B. Anderson, Melissa Maderia, Anthony J.A. Ouellette, Cindy Putnam-Evans, Lee Ann Higgins, Thomas Krick, Michael J. MacCoss, Hanjo Lim, John R. Yates, Bridgette A. Barry

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52 Scopus citations


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 A350PWLEPLR357 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.

Original languageEnglish (US)
Pages (from-to)14676-14681
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number23
StatePublished - Nov 12 2002


  • Collision-induced dissociation
  • Kynurenine
  • Mass spectrometry
  • Photoinhibition
  • Tryptophan


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