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X‐ray crystallographic structural studies of α‐amylase I from Eisenia fetida
Author(s) -
Hirano Yu,
Tsukamoto Kana,
Ariki Shingo,
Naka Yuki,
Ueda Mitsuhiro,
Tamada Taro
Publication year - 2020
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.374
H-Index - 138
ISSN - 2059-7983
DOI - 10.1107/s2059798320010165
Subject(s) - chemistry , amylase , mutant , enzyme , eisenia fetida , active site , substrate (aquarium) , crystallography , biochemistry , stereochemistry , biology , gene , ecology , organic chemistry , toxicity
The earthworm Eisenia fetida possesses several cold‐active enzymes, including α‐amylase, β‐glucanase and β‐mannanase. E. fetida possesses two isoforms of α‐amylase (Ef‐Amy I and II) to digest raw starch. Ef‐Amy I retains its catalytic activity at temperatures below 10°C. To identify the molecular properties of Ef‐Amy I, X‐ray crystal structures were determined of the wild type and of the inactive E249Q mutant. Ef‐Amy I has structural similarities to mammalian α‐amylases, including the porcine pancreatic and human pancreatic α‐amylases. Structural comparisons of the overall structures as well as of the Ca 2+ ‐binding sites of Ef‐Amy I and the mammalian α‐amylases indicate that Ef‐Amy I has increased structural flexibility and more solvent‐exposed acidic residues. These structural features of Ef‐Amy I may contribute to its observed catalytic activity at low temperatures, as many cold‐adapted enzymes have similar structural properties. The structure of the substrate complex of the inactive mutant of Ef‐Amy I shows that a maltohexaose molecule is bound in the active site and a maltotetraose molecule is bound in the cleft between the N‐ and C‐terminal domains. The recognition of substrate molecules by Ef‐Amy I exhibits some differences from that observed in structures of human pancreatic α‐amylase. This result provides insights into the structural modulation of the recognition of substrates and inhibitors.