Ono H, Gruhler A, Stuart R A, Guiard B, Schwarz E, Neupert W
Institut für Physiologische Chemie, Universität München, Federal Republic of Germany.
J Biol Chem. 1995 Jul 14;270(28):16932-8. doi: 10.1074/jbc.270.28.16932.
Precytochrome b2 is targeted to the mitochondrial intermembrane space by a dual targeting sequence comprising 80 amino acids. A kinetic analysis of intramitochondrial sorting was performed. The intermediate-size form accumulated transiently in the matrix. When import was performed in the presence of metal chelators to prevent the first processing by the matrix processing peptidase, > 40% of the imported precursor was localized in the matrix. A deletion of 13 amino acids in the intermembrane space sorting sequence caused partial inhibition of the first processing, and a transient accumulation of the precursor form in the matrix was also observed. The decrease in this matrix-localized precursor form paralleled an increase in the mature-size form in the intermembrane space. A point mutation in the mitochondrial targeting sequence (N-terminal to the sorting sequence) resulted in missorting to the matrix space. Furthermore, a chimeric protein consisting of the initial 85 residues of cytochrome b2 fused to dihydrofolate reductase was partially targeted to the matrix at 15 degrees C, but not at 25 degrees C. Together, the results presented here indicate that cytochrome b2 passes through the matrix on its sorting pathway to the intermembrane space.
细胞色素b2前体通过一个由80个氨基酸组成的双靶向序列被靶向定位于线粒体膜间隙。对线粒体内分选进行了动力学分析。中等大小的形式在基质中短暂积累。当在金属螯合剂存在下进行导入以防止基质加工肽酶的首次加工时，超过40%的导入前体定位于基质中。膜间隙分选序列中13个氨基酸的缺失导致首次加工部分受到抑制，并且还观察到前体形式在基质中的短暂积累。这种定位于基质的前体形式的减少与膜间隙中成熟大小形式的增加平行。线粒体靶向序列（分选序列的N端）中的一个点突变导致错误分选至基质空间。此外，由细胞色素b2的最初85个残基与二氢叶酸还原酶融合而成的嵌合蛋白在15℃时部分靶向至基质，但在25℃时则不然。总之，此处呈现的结果表明细胞色素b2在其分选至膜间隙的途径中穿过基质。
