講演会（The α-amylase families in CAZy – a bioinformatician’s view）開催報告
以下の講演会が 日本農芸化学会 北海道支部の補助を受け開催されました。
講演者所属： スロバキア科学アカデミー、University of SS Cyril and Methodius（スロバキア）
講演者氏名： Stefan Janecek 室長、教授
講演演題： The α-amylase families in CAZy
- a bioinformatician’s view.
日時： 2018年5月14日（月） 13：00～14：00
The specificity of α-amylase (EC 18.104.22.168), which hydrolyses the α-1,4-glucosidic linkages in starch and related α-glucans, is the best known representative of a large group of starch hydrolases and related amylolytic enzymes. The α-amylase family was originally created early in 1990s based on several crucial scientific observations, pioneering discoveries and efforts, such as sharing sequence similarities among different α-glucan-active enzymes within the same predicted fold of their catalytic domain, identifying the functionally versatile enzyme named neopullulanase and creating the classification of glycoside hydrolases (GHs) into sequence-based families. Currently, in fact, four GH families within the CAZy database might be considered the α-amylase families: (i) the main large α-amylase family GH13; (ii) the second smaller α-amylase family GH57; (iii) the family GH119; and (iv) probably also the family GH126. The main α-amylase family GH13 with more than 54 thousand sequences and about 30 different enzyme specificities belongs to the largest GH families. In addition to enzymes from hydrolases, transferases and isomerases, it contains also some non-enzymatic proteins involved in amino acid transport. The members of the α-amylase family GH13 employ a retaining reaction mechanism, share 4-7 conserved sequence regions (CSRs) and adopt a TIM-barrel domain with the GH13 catalytic machinery. Currently, the family is divided into 42 GH13 subfamilies, for which unique features in their amino acid sequences, i.e. sequence fingerprints, can be identified to be responsible for their individual specificities. The family GH13 forms, together with families GH70 and GH77, the clan GH-H; a remote homology of clan GH-H to family GH31 containing functionally related α-glucosidases being also already suggested. In comparison with GH13, the second α-amylase family GH57 is a smaller family with only about 2,000 members and less than 10 enzyme specificities. Although it also employs a retaining reaction mechanism, it exhibits its own 5 CSRs and catalytic machinery different from GH13 within an incomplete TIM-barrel catalytic domain fold. The individual enzyme specificities also possess unique features within their sequence logos that can be used as sequence-specificity fingerprints. A previous in silico analysis has suggested that the third α-amylase family GH119 should share the CSRs, catalytic machinery and fold of the catalytic domain with the family GH57. Finally, it is probable that the specificity of α-amylase is present also in the family GH126, although biochemical evidence is still unclear with regard to the endo- vs. exo-mode of action of the only characterized “amylase” from Clostridium perfringens, which, moreover, exhibits a structural homology with β-glucan-active enzymes employing inverting reaction mechanism. In addition to GH families reflecting classification based on catalytic domains, the so-called starch-binding domains of amylolytic enzymes classified among more than 10 carbohydrate-binding module (CBM) families, like CBM20, CBM21 and others, has attracted scientific interest, too. Thus thousands of protein sequences possessing tens of various amylolytic enzyme specificities from Bacteria, Archaea and Eucarya (some of them still waiting to be discovered) offer a scientific material worth of the in silico studies that subsequently could lead to their protein engineering and design.