A chloroplast processing enzyme involved in precursor maturation shares a zinc-binding motif with a recently recognized family of metalloendopeptidases.
A chloroplast processing enzyme involved in precursor maturation shares a zinc-binding motif with a recently recognized family of metalloendopeptidases.
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参与前体成熟的叶绿体加工酶与最近认识的金属内肽酶家族共享锌结合基序。
DOI：
10.1073/pnas.92.16.7177
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发表时间：
1995
影响因子：
11.1
通讯作者：
Lamppa,GK
中科院分区：
文献类型：
--
作者：
VanderVere,PS;Bennett,TM;Oblong,JE;Lamppa,GK
靶向叶绿体的核编码蛋白通常与N-末端转运肽合成，所述N-末端转运肽在输入时被蛋白水解去除。145和143 kDa的结构相关蛋白质与可溶性叶绿体加工酶（CPE）共纯化，所述可溶性叶绿体加工酶（CPE）切割主要捕光叶绿素a/B结合蛋白的前体，并且已经涉及核酮糖-1，5-二磷酸羧化酶/加氧酶和酰基载体蛋白的小亚基的成熟。145-和143-kDa的蛋白质还没有被发现作为异源二聚体，因此可能代表功能独立的亚型编码的不同基因。在这里，我们描述了一个140 kDa的多肽编码的cDNA分离，通过使用抗体提出的145/143 kDa的双联体的一级结构。该140-kDa多肽含有转运肽，并且引人注目地含有His-Xaa-Xaa-Glu-His锌结合基序，该基序在最近公认的金属内肽酶家族中是保守的，该家族包括大肠杆菌蛋白酶III、胰岛素降解酶和线粒体加工肽酶的亚基β。发现这些蛋白酶具有25- 30%的同一性，集中在140-kDa多肽的N末端附近。叶片中CPE的表达不依赖于光。事实上，转录本存在于黑暗生长的植物中，并且145/143-kDa的双联体和蛋白水解活性都存在于黄化体以及根质体中。因此，CPE似乎是光合和非光合组织中输入机制的必要组成部分，并且它可能在质体中起一般基质加工肽酶的作用。
Nuclear-encoded proteins targeted to the chloroplast are typically synthesized with N-terminal transit peptides which are proteolytically removed upon import. Structurally related proteins of 145 and 143 kDa copurify with a soluble chloroplast processing enzyme (CPE) that cleaves the precursor for the major light-harvesting chlorophyll a/b binding protein and have been implicated in the maturation of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase and acyl carrier protein. The 145- and 143-kDa proteins have not been found as a heterodimer and thus may represent functionally independent isoforms encoded by separate genes. Here we describe the primary structure of a 140-kDa polypeptide encoded by cDNAs isolated by using antibodies raised against the 145/143-kDa doublet. The 140-kDa polypeptide contains a transit peptide, and strikingly, a His-Xaa-Xaa-Glu-His zinc-binding motif that is conserved in a recently recognized family of metalloendopeptidases, which includes Escherichia coli protease III, insulin-degrading enzyme, and subunit beta of the mitochondrial processing peptidase. Identity of 25-30%, concentrated near the N terminus of the 140-kDa polypeptide, is found with these proteases. Expression of CPE in leaves is not light dependent. Indeed, transcripts are present in dark-grown plants, and the 145/143-kDa doublet and proteolytic activity are both found in etioplasts, as well as in root plastids. Thus, CPE appears to be a necessary component of the import machinery in photosynthetic and nonphotosynthetic tissues, and it may function as a general stromal processing peptidase in plastids.