Taguchi S, Kojima S, Terabe M, Kumazawa Y, Kohriyama H, Suzuki M, Miura K, Momose H
Department of Biological Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda-shi, Chiba 278, Japan.
J Mol Evol. 1997 May;44(5):542-51. doi: 10.1007/pl00006178.
We previously found that proteinaceous protease inhibitors homologous to Streptomyces subtilisin inhibitor (SSI) are widely produced by various Streptomyces species, and we designated them "SSI-like proteins" (Taguchi S, Kikuchi H, Suzuki M, Kojima S, Terabe M, Miura K, Nakase T, Momose H [1993] Appl Environ Microbiol 59:4338-4341). In this study, SSI-like proteins from five strains of the genus Streptoverticillium were purified and sequenced, and molecular phylogenetic trees were constructed on the basis of the determined amino acid sequences together with those determined previously for Streptomyces species. The phylogenetic trees showed that SSI-like proteins from Streptoverticillium species are phylogenetically included in Streptomyces SSI-like proteins but form a monophyletic group as a distinct lineage within the Streptomyces proteins. This provides an alternative phylogenetic framework to the previous one based on partial small ribosomal RNA sequences, and it may indicate that the phylogenetic affiliation of the genus Streptoverticillium should be revised. The phylogenetic trees also suggested that SSI-like proteins possessing arginine or methionine at the P1 site, the major reactive center site toward target proteases, arose multiple times on independent lineages from ancestral proteins possessing lysine at the P1 site. Most of the codon changes at the P1 site inferred to have occurred during the evolution of SSI-like proteins are consistent with those inferred from the extremely high G + C content of Streptomyces genomes. The inferred minimum number of amino acid replacements at the P1 site was nearly equal to the average number for all the variable sites. It thus appears that positive Darwinian selection, which has been postulated to account for accelerated rates of amino acid replacement at the major reaction center site of mammalian protease inhibitors, may not have dictated the evolution of the bacterial SSI-like proteins.
我们之前发现，与链霉菌枯草杆菌蛋白酶抑制剂（SSI）同源的蛋白质类蛋白酶抑制剂由多种链霉菌广泛产生，我们将它们命名为“类SSI蛋白”（田口S、菊池H、铃木M、小岛S、寺部M、三浦K、中濑T、桃瀬H [1993] 《应用与环境微生物学》59:4338 - 4341）。在本研究中，对来自轮生链霉菌属五个菌株的类SSI蛋白进行了纯化和测序，并基于所确定的氨基酸序列以及先前为链霉菌属物种所确定的氨基酸序列构建了分子系统发育树。系统发育树表明，来自轮生链霉菌属物种的类SSI蛋白在系统发育上包含在链霉菌类SSI蛋白中，但在链霉菌蛋白内作为一个独特的谱系形成一个单系群。这为基于部分小核糖体RNA序列的先前框架提供了一个替代的系统发育框架，并且可能表明轮生链霉菌属的系统发育归属应该修订。系统发育树还表明，在P1位点（对靶蛋白酶的主要反应中心位点）具有精氨酸或甲硫氨酸的类SSI蛋白，在独立谱系中从在P1位点具有赖氨酸的祖先蛋白多次产生。推断在类SSI蛋白进化过程中发生在P1位点的大多数密码子变化与从链霉菌基因组极高的G + C含量推断出的变化一致。推断在P1位点的最小氨基酸替换数几乎等于所有可变位点的平均数。因此，似乎为解释哺乳动物蛋白酶抑制剂主要反应中心位点氨基酸替换加速率而假定的正达尔文选择，可能并未决定细菌类SSI蛋白的进化。
