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  • Title: Phosphopeptides as substrates for thylakoid protein phosphatase activity.
    Author: Sun G, Sarath G, Markwell J.
    Journal: Arch Biochem Biophys; 1993 Aug 01; 304(2):490-5. PubMed ID: 8394059.
    Abstract:
    Lack of a suitable substrate has been a major obstacle in studying the chloroplastic thylakoid membrane protein phosphatase activity. In this study, the suitability of synthetic phosphopeptides for this purpose was investigated. Phosphothreonine-containing phosphopeptides mimicking the N-terminal phosphorylation site of the major thylakoid phosphoprotein, the light-harvesting chlorophyll a/b-binding protein (LHCP-II), were dephosphorylated by isolated peak thylakoid membranes. Phosphopeptides representing unrelated sequences or in which the target phosphothreonine had been changed to a phosphoserine were not dephosphorylated. The dephosphorylation of phosphopeptides by thylakoid membranes was similar to the dephosphorylation of endogenous LHCP-II in its pH-dependence profile, sensitivity to inhibitors, and bivalent cation requirement. The same phosphopeptide analogs of the LHCP-II phosphorylation site inhibited endogenous LHCP-II dephosphorylation in isolated thylakoids, whereas the dephospho-analogs and nonsubstrate phosphopeptides had no effect. Collectively, these results suggest that phosphopeptides mimicking a thylakoid phosphoprotein dephosphorylation site can be exploited for further study of the thylakoid protein phosphatase activity.
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