Bassham D C, Creighton A M, Arretz M, Brunner M, Robinson C
Department of Biological Sciences, University of Warwick, England.
Eur J Biochem. 1994 Apr 1;221(1):523-8. doi: 10.1111/j.1432-1033.1994.tb18764.x.
Cytosol-synthesized chloroplast and mitochondrial precursor proteins are proteolytically processed after import by highly specific, metal-dependent soluble enzymes: the stromal processing peptidase (SPP) and the matrix processing peptidase (MPP), respectively. We have used in vitro processing assays to compare the reaction specificities of highly purified preparations of pea SPP and Neurospora crassa MPP, both of which are unable to cleave a variety of 'foreign' proteins. We show that SPP can cleave all five mitochondrial precursor proteins tested, namely cyclophilin, the beta subunit of the F1-ATPase complex, the Rieske FeS protein, the alpha-MPP subunit and cytochrome b2. In contrast, MPP is unable to cleave any chloroplast precursor proteins tested. Several of the mitochondrial precursor proteins are cleaved more efficiently by SPP than are many authentic chloroplast precursor proteins but, in each case, cleavage takes place at a site or sites which are N-terminal to the authentic MPP site; pre-cyclophilin is cleaved 5 residues upstream of the MPP site and the precursor of the beta subunit of the F1-ATPase complex is cleaved at sites 5 and 12 residues upstream. We discuss the implications of these data for the SPP reaction mechanism.
胞质溶胶合成的叶绿体和线粒体前体蛋白在导入后会被高度特异性的、金属依赖性可溶性酶进行蛋白水解加工：分别是基质加工肽酶（SPP）和基质加工肽酶（MPP）。我们利用体外加工试验比较了豌豆SPP和粗糙脉孢菌MPP高度纯化制剂的反应特异性，这两种酶都无法切割多种“外来”蛋白质。我们发现SPP能够切割所测试的所有五种线粒体前体蛋白，即亲环蛋白、F1 - ATP酶复合体的β亚基、 Rieske FeS蛋白、α - MPP亚基和细胞色素b2。相比之下，MPP无法切割所测试的任何叶绿体前体蛋白。几种线粒体前体蛋白被SPP切割的效率比许多真正的叶绿体前体蛋白还要高，但在每种情况下，切割都发生在真正MPP切割位点的N端一个或多个位点；前亲环蛋白在MPP位点上游5个残基处被切割，F1 - ATP酶复合体β亚基的前体在MPP位点上游5个和12个残基处被切割。我们讨论了这些数据对SPP反应机制的影响。
