Roise D, Horvath S J, Tomich J M, Richards J H, Schatz G
EMBO J. 1986 Jun;5(6):1327-34. doi: 10.1002/j.1460-2075.1986.tb04363.x.
Subunit IV of yeast cytochrome oxidase is made in the cytoplasm with a transient pre-sequence of 25 amino acids which is removed upon import of the protein into mitochondria. To study the function of this cleavable pre-sequence in mitochondrial protein import, three peptides representing 15, 25 or 33 amino-terminal residues of the subunit IV precursor were chemically synthesized. All three peptides were freely soluble in aqueous buffers, yet inserted spontaneously from an aqueous subphase into phospholipid monolayers up to an extrapolated limiting monolayer pressure of 40-50 mN/m. The two longer peptides also caused disruption of unilamellar liposomes. This effect was increased by a diffusion potential, negative inside the liposomes, and decreased by a diffusion potential of opposite polarity. The peptides, particularly the two longer ones, also uncoupled respiratory control of isolated yeast mitochondria. The 25-residue peptide had little secondary structure in aqueous buffer but became partly alpha-helical in the presence of detergent micelles. Based on the amino acid sequence of the peptides, a helical structure would have a highly asymmetric distribution of charged and apolar residues and would be surface active. Amphiphilic helicity appears to be a general feature of mitochondrial pre-sequences. We suggest that this feature plays a crucial role in transporting proteins into mitochondria.
酵母细胞色素氧化酶的亚基IV在细胞质中合成，带有一段25个氨基酸的短暂前导序列，该序列在蛋白质导入线粒体时被去除。为了研究这种可裂解前导序列在线粒体蛋白质导入中的功能，化学合成了代表亚基IV前体15、25或33个氨基末端残基的三种肽。所有这三种肽都能自由溶解于水性缓冲液中，但能从水相自发插入磷脂单分子层，直至外推极限单分子层压力达到40 - 50 mN/m。两种较长的肽还会导致单层脂质体破裂。脂质体内部为负的扩散电位会增强这种效应，而相反极性的扩散电位则会减弱这种效应。这些肽，尤其是两种较长的肽，还会解除分离的酵母线粒体的呼吸控制。25个残基的肽在水性缓冲液中几乎没有二级结构，但在去污剂胶束存在时会部分形成α螺旋。根据肽的氨基酸序列，螺旋结构会有带电和非极性残基的高度不对称分布，并且具有表面活性。两亲性螺旋似乎是线粒体前导序列的一个普遍特征。我们认为这一特征在将蛋白质转运到线粒体中起着关键作用。
