title: Calcium ion-dependent increase in thermostability of dextran glucosidase from Streptococcus mutans.
abstract: Dextran glucosidase from Streptococcus mutans (SmDG), which belongs to glycoside hydrolase family 13 (GH13), hydrolyzes the non-reducing terminal glucosidic linkage of isomaltooligosaccharides and dextran. Thermal deactivation of SmDG did not follow the single exponential decay but rather the two-step irreversible deactivation model, which involves an active intermediate having 39% specific activity. The presence of a low concentration of CaCl2 increased the thermostability of SmDG, mainly due to a marked reduction in the rate constant of deactivation of the intermediate. The addition of MgCl2 also enhanced thermostability, while KCl and NaCl were not effective. Therefore, divalent cations, particularly Ca2+, were considered to stabilize SmDG. On the other hand, CaCl2 had no significant effect on catalytic reaction. The enhanced stability by Ca2+ was probably related to calcium binding in the β→α loop 1 of the (β/α)(8) barrel of SmDG. Because similar structures and sequences are widespread in GH13, these GH13 enzymes might have been stabilized by calcium ions.
authors.affiliation: Research Faculty of Agriculture, Hokkaido University, Sapporo, Japan.
authors.forename: Momoko
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Hironori
authors.initials: H
authors.lastname: Hondoh
authors.forename: Haruhide
authors.initials: H
authors.lastname: Mori
authors.forename: Wataru
authors.initials: W
authors.lastname: Saburi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Okuyama
authors.forename: Atsuo
authors.initials: A
authors.lastname: Kimura
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D003001:Cloning, Molecular; D003911:Dextrans / Q000378:metabolism*; D004795:Enzyme Stability / Q000187:drug effects; D004926:Escherichia coli; D005959:Glucosidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008958:Models, Molecular; D009844:Oligosaccharides / Q000378:metabolism*; D010957:Plasmids; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013295:Streptococcus mutans / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002413:Cations, Divalent; D003911:Dextrans; D009844:Oligosaccharides; D011994:Recombinant Proteins; C021705:maltooligosaccharides; D005959:Glucosidases; C023149:exo-1,6-alpha-glucosidase; D008274:Magnesium; D002118:Calcium