Calcium Ion Contribution to Thermostability of Cyclodextrin Glycosyltransferase Is Closely Related to Calcium-Binding Site CaIII

摘要

In the study, we investigated the contribution of Ca~(2+) to the thermostability of α-cyclodextrin glycosyltransferase (α-CGTase) from Paenibacillus macerans, which has two calcium-binding sites (Cal and Call), and β-CGTase from Bacillus circulans, which contains an additional calcium-binding site (Calll), consisting of Ala315 and Asp577. It was found that the contribution of Ca~(2+) to the thermostability of two CGTases displayed a marked difference. Ca~(2+) affected β-CGTase thermostability significantly. After Ca~(2+) was added to β-CGTase solution to a final concentration of 5 mM followed by incubation for 120 min at 60 °C, residual activity of β-CGTase was 88.3%, which was much higher than that without Ca~(2+). However, Ca~(2+) had a small contribution to α-CGTase thermostability. Furthermore, A31SD and D577K mutations at Calll could significantly change the contribution of Ca~(2+) to β-CGTase thermostability. These results suggested that the contribution of Ca~(2+) to CGTase thermostability was closely related to Calll.