The present study deals with the genetic changes observed in the protein sequence of an α-amylase from Streptomyces spp. and its structural homologs from Pseudoalteromonas haloplanktis, invertebrates and mammals. The structural homologs are renowned for their important features such as chloride binding triad and a serine-protease like catalytic triad (a triad which is reported to be strictly conserved in all chloride-dependent α-amylases). These conserved regions are essential for allosteric activation of enzyme and conformational stability, respectively. An evaluation of these distinctive features in Streptomyces α-amylases revealed the role of mutations in conserved regions and evolution of chloride-independent α-amylases in Streptomyces spp. Besides, the study also discovers a highly divergent α-amylase from Streptomyces spp. which varies greatly even within the homologs of the same genus. Another very important feature is the number of disulfide bridges in which the structural homologs own eight Cys residues to form four disulfide bridges whereas Streptomyces α-amylases possess only seven Cys to form three disulfide bridges. The study also highlights the unique evolution of carbohydrate binding module 20 domain (CBM20 also known as raw starch binding domain or E domain) in Streptomyces α-amylases which is completely absent in α-amylases of other structural homologs.

本研究处理了链霉菌α-淀粉酶蛋白序列中观察到的遗传变化。和其结构同源物来自假单胞菌，无脊椎动物和哺乳动物。结构同系物以其重要特征而闻名，例如氯结合三联体和丝氨酸蛋白酶催化三联体（据报道，三联体在所有依赖氯的α-淀粉酶中都严格保守）。这些保守区分别对于酶的变构活化和构象稳定性是必不可少的。对链霉菌α-淀粉酶中这些独特特征的评估揭示了保守区中突变的作用以及链霉菌中不依赖氯离子的α-淀粉酶的进化spp。此外，该研究还发现链霉菌属（Streptomyces spp）的α-淀粉酶高度不同。即使在同一属的同源物中，其变化也很大。另一个非常重要的特征是二硫键的数量，其中结构同系物拥有八个Cys残基以形成四个二硫键，而链霉菌α-淀粉酶仅具有七个Cys来形成三个二硫键。该研究还强调了链霉菌α-淀粉酶中碳水化合物结合模块20结构域（CBM20，也称为生淀粉结合结构域或E结构域）的独特进化，而其他结构同源物的α-淀粉酶则完全不存在。