Department of Plant Sciences, University of California, Davis, California, USA.
Plant Signal Behav. 2010 Jun;5(6):721-3. doi: 10.4161/psb.5.6.11662.
Thylakoidal processing peptidase (TPP) catalyzes the removal of signal peptide which leads to maturation of a subset of proteins including photosynthetic electron transport components in thylakoids. The biochemical properties of TPP were highly defined during the 1980's and 1990's, but the physiological significance of the TPP activity had remained undefined. Completion of genome sequencing revealed the presence of three TPP isoforms in the model plant Arabidopsis thaliana. A recent genetic study demonstrated that one isoform, plastidic type I signal peptidase 1 (Plsp1), is necessary for proper thylakoid assembly. Interestingly, Plsp1 was found in both the chloroplast envelope and thylakoids, being responsible for maturation of an outer membrane protein Toc75 and a lumenal protein OE33. A more recent study has shown that Plsp1 is involved in maturation of two additional lumenal proteins, OE23 and plastocyanin, and that accumulation of unprocessed Toc75 does not disrupt normal chloroplast development. The study also revealed that plsp1-null plastids accumulate balloon-like vesicles that appear to be the remnants of thylakoids as they contain unprocessed OE33 in the peripheral regions. These findings suggest that proper maturation of lumenal proteins is required for correct assembly and/or maintenance of thylakoids, but may not be necessary for initiation of membrane development. The ballooned thylakoids in plsp1-null plastids may be a useful tool to elucidate the mechanism of thylakoid flattening, which correlates with the energized state of the membranes.
类囊体加工肽酶（TPP）催化信号肽的去除，从而成熟包括类囊体中的光合电子传递成分在内的蛋白质亚类。TPP 的生化特性在 20 世纪 80 年代和 90 年代得到了高度定义，但 TPP 活性的生理意义仍然没有定义。基因组测序的完成揭示了模式植物拟南芥中存在三种 TPP 同工型。最近的一项遗传研究表明，一种同工型，质体型 I 信号肽酶 1（Plsp1），对于类囊体的正确组装是必要的。有趣的是，Plsp1 存在于叶绿体包膜和类囊体中，负责成熟外膜蛋白Toc75 和腔蛋白 OE33。最近的一项研究表明，Plsp1 参与成熟另外两种腔蛋白 OE23 和质体蓝素，并且未加工的Toc75 的积累不会破坏正常的叶绿体发育。该研究还表明，plsp1 缺失的质体积累气球状囊泡，这些囊泡似乎是类囊体的残留物，因为它们在周边区域含有未加工的 OE33。这些发现表明，腔蛋白的正确成熟对于类囊体的正确组装和/或维持是必需的，但对于膜发育的起始可能不是必需的。plsp1 缺失的质体中的气球状类囊体可能是阐明类囊体扁平化机制的有用工具，类囊体扁平化与膜的能量状态相关。
