On the molecular mechanism of light-induced D1 protein degradation in photosystem II core particles.
On the molecular mechanism of light-induced D1 protein degradation in photosystem II core particles.
复制标题
光系统II核心颗粒中光诱导D1蛋白降解的分子机制。
作者：
A. Salter;I. Virgin;Aasa Hagman;B. Andersson
在光抑制光照条件下，研究了D1蛋白降解的机制。研究表明，蛋白质水解活性存在于光系统II核心复合物中。D1蛋白降解的抑制与高度特异性丝氨酸蛋白酶抑制剂氟磷酸二异丙基与光系统II分离的复合物的结合之间存在关系，证明该蛋白酶属于丝氨酸类型。利用放射性标记抑制剂发现，代表催化位点活性丝氨酸的结合位点位于一个43-kDa的多肽上，可能是叶绿素a蛋白CP43。蛋白酶在黑暗中明显活跃，分解的起始依赖于强光诱导的底物激活。蛋白水解在pH 7.5时达到最佳，产生23和16 kDa的初级降解片段。此外，还鉴定了14、13和10 kDa的D1蛋白片段。磷酸标记的D1蛋白和序列特异性抗血清实验表明，23- kda和16-kDa片段分别来自N端和c端，这表明D1蛋白在跨膜螺旋D和E之间的外类囊体表面发生了初级切割。
The mechanism of D1 protein degradation was investigated during photoinhibitory illumination of isolated photosystem II core preparations. The studies revealed that a proteolytic activity resides within the photosystem II core complex. A relationship between the inhibition of D1 protein degradation and the binding of the highly specific serine protease inhibitor diisopropyl fluorophosphate to isolated complexes of photosystem II was observed, evidence that this protease is of the serine type. Using radiolabeled inhibitor, it was shown that the binding site, representing the active serine of the catalytic site, is located on a 43-kDa polypeptide, probably the chlorophyll a protein CP43. The protease is apparently active in darkness, with the initiation of breakdown being dependent on high light-induced substrate activation. The proteolysis, which has an optimum at pH 7.5, gives rise to primary degradation fragments of 23 and 16 kDa. In addition, D1 protein fragments of 14, 13, and 10 kDa were identified. Experiments with phosphate-labeled D1 protein and sequence-specific antisera showed that the 23- and 16-kDa fragments originate from the N- and C-termini, respectively, suggesting a primary cleavage of the D1 protein at the outer thylakoid surface in the region between transmembrane helices D and E.