Teixeira Pedro Filipe, Glaser Elzbieta
Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-106 91 Stockholm, Sweden.
Biochim Biophys Acta. 2013 Feb;1833(2):360-70. doi: 10.1016/j.bbamcr.2012.03.012. Epub 2012 Apr 1.
Most of the mitochondrial and chloroplastic proteins are nuclear encoded and synthesized in the cytosol as precursor proteins with N-terminal extensions called targeting peptides. Targeting peptides function as organellar import signals, they are recognized by the import receptors and route precursors through the protein translocons across the organellar membranes. After the fulfilled function, targeting peptides are proteolytically cleaved off inside the organelles by different processing peptidases. The processing of mitochondrial precursors is catalyzed in the matrix by the Mitochondrial Processing Peptidase, MPP, the Mitochondrial Intermediate Peptidase, MIP (recently called Octapeptidyl aminopeptidase 1, Oct1) and the Intermediate cleaving peptidase of 55kDa, Icp55. Furthermore, different inner membrane peptidases (Inner Membrane Proteases, IMPs, Atp23, rhomboids and AAA proteases) catalyze additional processing functions, resulting in intra-mitochondrial sorting of proteins, the targeting to the intermembrane space or in the assembly of proteins into inner membrane complexes. Chloroplast targeting peptides are cleaved off in the stroma by the Stromal Processing Peptidase, SPP. If the protein is further translocated to the thylakoid lumen, an additional thylakoid-transfer sequence is removed by the Thylakoidal Processing Peptidase, TPP. Proper function of the D1 protein of Photosystem II reaction center requires its C-terminal processing by Carboxy-terminal processing protease, CtpA. Both in mitochondria and in chloroplasts, the cleaved targeting peptides are finally degraded by the Presequence Protease, PreP. The organellar proteases involved in precursor processing and targeting peptide degradation constitute themselves a quality control system ensuring the correct maturation and localization of proteins as well as assembly of protein complexes, contributing to sustenance of organelle functions. Dysfunctions of several mitochondrial processing proteases have been shown to be associated with human diseases. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
大多数线粒体和叶绿体蛋白质是由核基因编码，并在细胞质中作为具有N端延伸序列（称为靶向肽）的前体蛋白进行合成。靶向肽作为细胞器导入信号，被导入受体识别，并引导前体蛋白通过蛋白质转运体穿过细胞器膜。在完成功能后，靶向肽在细胞器内被不同的加工肽酶通过蛋白水解作用切除。线粒体前体蛋白的加工由线粒体加工肽酶（MPP）、线粒体中间肽酶（MIP，最近称为八肽基氨肽酶1，Oct1）和55kDa的中间切割肽酶（Icp55）在基质中催化。此外，不同的内膜肽酶（内膜蛋白酶，IMPs，Atp23、菱形蛋白酶和AAA蛋白酶）催化额外的加工功能，导致蛋白质在线粒体内分选、靶向到膜间隙或蛋白质组装到内膜复合物中。叶绿体靶向肽在基质中被基质加工肽酶（SPP）切除。如果蛋白质进一步转运到类囊体腔中，一个额外的类囊体转移序列会被类囊体加工肽酶（TPP）去除。光系统II反应中心D1蛋白的正常功能需要其C端由羧基末端加工蛋白酶（CtpA）进行加工。在线粒体和叶绿体中，切割后的靶向肽最终都由前序列蛋白酶（PreP）降解。参与前体加工和靶向肽降解的细胞器蛋白酶本身构成了一个质量控制系统，确保蛋白质的正确成熟和定位以及蛋白质复合物的组装，有助于维持细胞器的功能。几种线粒体加工蛋白酶的功能障碍已被证明与人类疾病有关。本文是名为：线粒体和质体中的蛋白质导入与质量控制的特刊的一部分。
