Degradation of periplasmic proteins (Deg)/high temperature requirement A (HtrA) proteases are ATP-independent Ser endopeptidases that perform key aspects of protein quality control in all domains of life. Here, we characterized Chlamydomonas reinhardtii DEG1C, which together with DEG1A and DEG1B is orthologous to Arabidopsis (Arabidopsis thaliana) Deg1 in the thylakoid lumen. We show that DEG1C is localized to the stroma and the periphery of thylakoid membranes. Purified DEG1C exhibited high proteolytic activity against unfolded model substrates and its activity increased with temperature and pH. DEG1C forms monomers, trimers, and hexamers that are in dynamic equilibrium. DEG1C protein levels increased upon nitrogen, sulfur, and phosphorus starvation; under heat, oxidative, and high light stress; and when Sec-mediated protein translocation was impaired. DEG1C depletion was not associated with any obvious aberrant phenotypes under nonstress conditions, high light exposure, or heat stress. However, quantitative shotgun proteomics revealed differences in the abundance of 307 proteins between a deg1c knock-out mutant and the wild type under nonstress conditions. Among the 115 upregulated proteins are PSII biogenesis factors, FtsH proteases, and proteins normally involved in high light responses, including the carbon dioxide concentrating mechanism, photorespiration, antioxidant defense, and photoprotection. We propose that the lack of DEG1C activity leads to a physiological state of the cells resembling that induced by high light intensities and therefore triggers high light protection responses.

中文翻译：

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衣藻 deg1c 突变体积累参与高光驯化的蛋白质。

周质蛋白 (Deg) 降解/高温要求 A (HtrA) 蛋白酶是 ATP 独立的 Ser 内肽酶，在生命的各个领域执行蛋白质质量控​​制的关键方面。在这里，我们表征了莱茵衣藻 DEG1C，它与 DEG1A 和 DEG1B 一起与类囊体腔中的拟南芥 (Arabidopsis thaliana) Deg1 是直系同源的。我们发现 DEG1C 定位于基质和类囊体膜的外围。纯化的 DEG1C 对未折叠的模型底物表现出高蛋白水解活性，并且其活性随着温度和 pH 值的增加而增加。DEG1C 形成处于动态平衡的单体、三聚体和六聚体。DEG1C 蛋白质水平在氮、硫和磷饥饿时增加；在热、氧化和强光胁迫下；当 Sec 介导的蛋白质易位受损时。在非应激条件、高光暴露或热应激下，DEG1C 消耗与任何明显的异常表型无关。然而，定量鸟枪法蛋白质组学揭示了非应激条件下 deg1c 敲除突变体和野生型之间 307 蛋白丰度的差异。115 种上调的蛋白质包括 PSII 生物发生因子、FtsH 蛋白酶和通常参与高光响应的蛋白质，包括二氧化碳浓缩机制、光呼吸、抗氧化防御和光保护。我们认为 DEG1C 活性的缺乏会导致细胞出现类似于高光强度诱导的生理状态，从而触发高光保护反应。