Palmieri F, Bisaccia F, Capobianco L, Dolce V, Fiermonte G, Iacobazzi V, Zara V
Department of Pharmaco-Biology, University of Bari, Italy.
J Bioenerg Biomembr. 1993 Oct;25(5):493-501. doi: 10.1007/BF01108406.
Phosphate and oxoglutarate carriers transport phosphate and oxoglutarate across the inner membranes of mitochondria in exchange for OH- and malate, respectively. Both carriers belong to the mitochondrial carrier protein family, characterized by a tripartite structure made up of related sequences about 100 amino acids in length. The results obtained on the topology of the phosphate and oxoglutarate carriers are consistent with the six alpha-helix model proposed by Saraste and Walker. In both carriers the N- and C-terminal regions are exposed toward the cytosol. In addition, the oxoglutarate carrier has been shown to be a dimer by means of crosslinking studies. The bovine and human genes coding for the oxoglutarate carrier are split into eight and six exons, respectively, and five introns are found to the same position in both genes. The bovine and human phosphate carrier genes have the same organization with nine exons separated by eight introns at exactly the same positions. The phosphate carrier of mammalian mitochondria is synthesized with a cleavable presequence, in contrast to the oxoglutarate carrier and the other members of the mitochondrial carrier family. The precursor of the phosphate carrier is efficiently imported, proteolytically processed, and correctly assembled in isolated mitochondria. The presequence-deficient phosphate carrier is imported with an efficiency of about 50% as compared with the precursor of the phosphate carrier and is correctly assembled, demonstrating that the mature portion of the phosphate carrier contains sufficient information for import and assembly into mitochondria.
磷酸和草酰戊二酸载体分别将磷酸和草酰戊二酸转运过线粒体内膜，以交换OH-和苹果酸。这两种载体都属于线粒体载体蛋白家族，其特征是由长度约为100个氨基酸的相关序列组成的三重结构。关于磷酸和草酰戊二酸载体拓扑结构的研究结果与萨拉斯特和沃克提出的六螺旋模型一致。在这两种载体中，N端和C端区域都朝向胞质溶胶暴露。此外，通过交联研究表明草酰戊二酸载体是二聚体。编码草酰戊二酸载体的牛和人基因分别被分成八个和六个外显子，并且在两个基因的相同位置发现了五个内含子。牛和人的磷酸载体基因具有相同的组织形式，九个外显子被八个内含子分隔，且内含子位置完全相同。与草酰戊二酸载体和线粒体载体家族的其他成员不同，哺乳动物线粒体的磷酸载体在合成时带有一个可裂解的前导序列。磷酸载体的前体能够有效地导入、进行蛋白水解加工并在分离的线粒体中正确组装。与磷酸载体前体相比，缺乏前导序列的磷酸载体的导入效率约为50%，并且能够正确组装，这表明磷酸载体的成熟部分包含足够的信息用于导入和组装到线粒体中。
