Isaya G, Kalousek F, Fenton W A, Rosenberg L E
Yale University School of Medicine, Department of Human Genetics, New Haven, Connecticut 06510.
J Cell Biol. 1991 Apr;113(1):65-76. doi: 10.1083/jcb.113.1.65.
Many precursors of mitochondrial proteins are processed in two successive steps by independent matrix peptidases (MPP and MIP), whereas others are cleaved in a single step by MPP alone. To explain this dichotomy, we have constructed deletions of all or part of the octapeptide characteristic of a twice cleaved precursor (human ornithine transcarbamylase [pOTC]), have exchanged leader peptide sequences between once-cleaved (human methylmalonyl-CoA mutase [pMUT]; yeast F1ATPase beta-subunit [pF1 beta]) and twice-cleaved (pOTC; rat malate dehydrogenase (pMDH); Neurospora ubiquinol-cytochrome c reductase iron-sulfur subunit [pFe/S]) precursors, and have incubated these proteins with purified MPP and MIP. When the octapeptide of pOTC was deleted, or when the entire leader peptide of a once-cleaved precursor (pMUT or pF1 beta) was joined to the mature amino terminus of a twice-cleaved precursor (pOTC or pFe/S), no cleavage was produced by either protease. Cleavage of these constructs by MPP was restored by re-inserting as few as two amino-terminal residues of the octapeptide or of the mature amino terminus of a once-cleaved precursor. We conclude that the mature amino terminus of a twice-cleaved precursor is structurally incompatible with cleavage by MPP; such proteins have evolved octapeptides cleaved by MIP to overcome this incompatibility.
许多线粒体蛋白前体由独立的基质肽酶（MPP和MIP）分两步连续加工，而其他一些则仅由MPP一步切割。为了解释这种二分法，我们构建了完全缺失或部分缺失二次切割前体（人鸟氨酸转氨甲酰酶[pOTC]）特征性八肽的缺失体，在一次切割（人甲基丙二酰辅酶A变位酶[pMUT]；酵母F1ATP酶β亚基[pF1β]）和二次切割（pOTC；大鼠苹果酸脱氢酶[pMDH]；粗糙脉孢菌泛醇-细胞色素c还原酶铁硫亚基[pFe/S]）前体之间交换前导肽序列，并将这些蛋白质与纯化的MPP和MIP一起孵育。当pOTC的八肽缺失时，或者当一次切割前体（pMUT或pF1β）的整个前导肽连接到二次切割前体（pOTC或pFe/S）的成熟氨基末端时，两种蛋白酶均未产生切割。通过重新插入八肽或一次切割前体成熟氨基末端的少至两个氨基末端残基，可恢复MPP对这些构建体的切割。我们得出结论，二次切割前体的成熟氨基末端在结构上与MPP切割不相容；此类蛋白质已进化出由MIP切割的八肽以克服这种不相容性。
