Journal
PROTEOMICS
Volume 12, Issue 18, Pages 2852-2861Publisher
WILEY-BLACKWELL
DOI: 10.1002/pmic.201200196
Keywords
Maize; Mass spectrometry; Phosphoproteomics; Phosphorylation stoichiometry; Plant proteomics; Thylakoid membranes
Funding
- Swedish Research Council [2008-5490]
- Ministry of Science and High Education of Poland [NN 303 393636]
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In C4 plants, such as maize, the photosynthetic apparatus is partitioned over two cell types called mesophyll (M) and bundle sheath (BS), which have different structure and specialization of the photosynthetic thylakoid membranes. We characterized protein phosphorylation in thylakoids of the two cell types from maize grown under either low or high light. Western blotting with phosphothreonine antibodies and ProQ phosphostaining detected light-dependent changes in the protein phosphorylation patterns. LC-MS/MS with alternating CID and electron transfer dissociation sequencing of peptide ions mapped 15 protein phosphorylation sites. Phosphorylated D2, CP29, CP26, Lhcb2 proteins, and ATPsynthase were found only in M membranes. A previously unknown phosphorylation site was mapped in phosphoenolpyruvate carboxykinase from the BS cells. Phosphorylation stoichiometry was calculated from the ratios of normalized ion currents for phosphorylated to nonphosphorylated peptide pairs from the D1, D2, CP43, and PbsH proteins of photosystem II (PSII). Every PSII in M thylakoids contained on average 1.5 +/- 0.1 or 2.3 +/- 0.2 phosphoryl groups in plants grown under either low or high light, while in BS membranes the corresponding numbers were 0.25 +/- 0.1 or 0.7 +/- 0.2, respectively. It is suggested that the phosphorylation level, as well as turnover of PSII depend on the structure of thylakoids.
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