α-Amylase catalyzes the endohydrolysis of α-1,4-glucosidic linkages in starch and related α-glucans. In the CAZy database, most α-amylases have been classified into the family GH13 counting at present more than 80,000 sequences and ~ 30 different enzyme specificities. The family has already been divided into 42 subfamilies, but additional subfamilies are still emerging. The present bioinformatics study was undertaken in an effort to propose a novel GH13 subfamily around the experimentally characterized α-amylase from the halophilic archaeon Haloarcula hispanica, which until now has not been assigned to any GH13 subfamily. The in silico analysis resulted in collecting a convincing group of putative haloarchaeal α-amylase homologues sharing sequence similarities mainly in their conserved sequence regions (CSRs) and forming a cluster in the evolutionary tree, which is well separated from representatives of established GH13 subfamilies. One of the most exclusive sequence features of the novel GH13 subfamily is the tyrosine (Tyr79 in H. hispanica α-amylase numbering) succeeding the glycine at the beginning of the CSR-VI at the β2 strand of the catalytic TIM-barrel. Evolutionarily, the novel GH13 α-amylase subfamily was most closely related to two clusters of GH13 subfamilies with the specificity of α-amylase, i.e. subfamilies GH13_5, 6 and 7 as well as GH13_15, 24, 27 and 28.

中文翻译：

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一个新的GH13亚家族，由嗜盐古细菌Haloarcula hispanica的α-淀粉酶代表。

α-淀粉酶催化淀粉和相关α-葡聚糖中α-1,4-糖苷键的内水解。在CAZy数据库中，大多数α-淀粉酶已被分类为GH13家族，目前计数超过80,000个序列和约30种不同的酶特异性。该家族已被划分为42个亚家族，但仍在出现其他亚家族。进行本生物信息学研究的目的是围绕嗜盐古细菌Haloarcula hispanica的实验表征的α-淀粉酶，提出一个新的GH13亚家族。，到目前为止，尚未将其分配给任何GH13子家族。通过计算机分析，收集了令人信服的一组假定的卤代古细菌α-淀粉酶同源物，这些同源物主要在其保守序列区（CSR）中共享序列相似性，并在进化树中形成了一个簇，该簇与已建立的GH13亚家族的代表相距甚远。新型GH13亚家族最独特的序列特征之一是酪氨酸（H. hispanica中的Tyr79CSR-VI起始处在催化TIM-桶的β2链后接甘氨酸的α-淀粉酶编号。在进化上，新型GH13α-淀粉酶亚家族与两个具有α-淀粉酶特异性的GH13亚家族最紧密相关，即GH13_5、6和7以及GH13_15、24、27和28。