Calcium Ion-Dependent Increase in Thermostability of Dextran Glucosidase fromStreptococcus mutans

Momoko KOBAYASHI, Hironori HONDOH, Haruhide MORI, Wataru SABURI, Masayuki OKUYAMA, Atsuo KIMURA
2011 Bioscience, biotechnology and biochemistry  
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 CaCl 2 increased the thermostability of SmDG, mainly due
more » ... of SmDG, mainly due to a marked reduction in the rate constant of deactivation of the intermediate. The addition of MgCl 2 also enhanced thermostability, while KCl and NaCl were not effective. Therefore, divalent cations, particularly Ca 2þ , were considered to stabilize SmDG. On the other hand, CaCl 2 had no significant effect on catalytic reaction. The enhanced stability by Ca 2þ was probably related to calcium binding in the ! loop 1 of the ð=Þ 8 barrel of SmDG. Because similar structures and sequences are widespread in GH13, these GH13 enzymes might have been stabilized by calcium ions.
doi:10.1271/bbb.110256 pmid:21821929 fatcat:w5h3ur5i5jf67i7oh5x6hpxzz4