Tyystjärvi T, Aro E M, Jansson C, Mäenpää P
Department of Biology, University of Turku, Finland.
Plant Mol Biol. 1994 Jun;25(3):517-26. doi: 10.1007/BF00043879.
The degradation rate of the D1 polypeptide was measured in three Synechocystis PCC 6803 mutants in 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 [delta (E242-E244);Q241H] and E243K, and the third mutation, E229D, was directed to the PEST-like area. During high-light illumination (1500 mumol photons m-2 s-1) that induced photoinhibition of photosystem II (PSII), the half-life time of the D1 polypeptide in mutant E229D (t 1/2 = 35 min) was about twice as long as in AR (control strain) cells (t 1/2 = 19 min). In growth light (40 mumol photons m-2 s-1), the degradation rate of the D1 polypeptide in E229D and AR strains was the same (t 1/2 approximately 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.
在体内测量了三个集胞藻PCC 6803突变体中D1多肽的降解速率。将突变引入D1多肽的一个假定切割区域（QEEET基序）和类PEST区域。PEST序列经常出现在周转率高的蛋白质中。QEEET基序突变体为CA1[缺失（E242 - E244）；Q241H]和E243K，第三个突变E229D则针对类PEST区域。在诱导光系统II（PSII）光抑制的高光照射（1500 μmol光子 m⁻² s⁻¹）期间，突变体E229D中D1多肽的半衰期（t 1/2 = 35分钟）约为AR（对照菌株）细胞中（t 1/2 = 19分钟）的两倍。在生长光（40 μmol光子 m⁻² s⁻¹）下，E229D和AR菌株中D1多肽的降解速率相同（t 1/2约为5小时）。在生长光下，两个QEEET基序突变体中D1多肽的降解速度都比AR菌株快，但在光抑制光下，降解速率相似。根据这些结果，高度保守的QEEET基序本身并非D1多肽蛋白水解切割所必需，但它确实会影响降解速率。在我们的实验条件下，突变体和AR细胞中D1多肽的降解速率与PSII对光抑制的敏感性之间不存在简单的相关性。
