Changes of amino acid sequence in PEST-like area and QEEET motif affect degradation rate of D1 polypeptide in photosystem II |
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Authors: | Taina Tyystjärvi Eva-Mari Aro Christer Jansson Pirkko Mäenpää |
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Affiliation: | (1) Department of Biology, University of Turku, BioCity A 6th floor, Tykistökatu 6, FIN-20520 Turku, Finland;(2) Department of Biochemistry, University of Stockholm, S-10691 Stockholm, Sweden |
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Abstract: | The degradation rate of the D1 polypeptide was measured in threeSynechocystis PCC 6803 mutantsin vivo. Mutations were introduced into a putative cleavage area of the D1 polypeptide (QEEET motif) and into the PEST-like area. PEST sequences are often found in proteins with a high turnover rate. The QEEET-motif mutants are CA1 [ (E242-E244);Q241H] and E243K, and the third mutation, E229D, was directed to the PEST-like area. During high-light illumination (1500 mol photons m-2s-1) that induced photoinhibition of photosystem II (PSII), the half-life time of the D1 polypeptide in mutant E229D (t1/2=35 min) was about twice as long as in AR (control strain) cells (t1/2=19 min). In growth light (40 mol photons m-2s-1), the degradation rate of the D1 polypeptide in E229D and AR strains was the same (t1/2 5 h). In growth light the D1 polypeptide was degraded faster in both QEEET-motif mutants than in the AR strain, but in photoinhibitory light the degradation rates were similar. According to these results, the highly conservative QEEET motif as such is not required for the proteolytic cut of the D1 polypeptide, but it does affect the rate of degradation. No simple correlation existed between the degradation rate of the D1 polypeptide and the susceptibility of PSII to photoinhibition in mutant and AR cells under our experimental conditions. |
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Keywords: | D1 polypeptide photoinhibition photosystem II protein turnover site-specific mutants Synechocystis 6803 |
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