Calcium and sodium ions synergistically enhance the thermostability of a maltooligosaccharide-forming amylase from Bacillus stearothermophilus STB04

•Bst-MFAse, an amylase, hydrolyzes starch into functional maltooligosaccharides.•Ca2+ and Na+ synergistically enhance the thermostability of Bst-MFAse at 80 °C.•Protein modeling reveals an important Ca2+–Na+–Ca2+ binding site in its structure.•Ca2+ and Na+ synergistically protect the secondary structure of Bst-MFAse.•Ca2+ and Na+ synergistically protect the tertiary structure of Bst-MFAse. Maltooligosaccharide-forming amylases (MFAses) are promising tools for a variety of food industry applications because of their ability to hydrolyze starch into maltooligosaccharides. However, high thermostability is a key requirement for enzymes used in these applications. In this work, we investigated the effect of Ca2+ and Na+ on the thermostability of an MFAse from Bacillus stearothermophilus (Bst-MFAse). The results showed that Ca2+ and Na+ synergistically prolong the half-life of Bst-MFAse. The most significant improvement, which preserved 71.1% of initial activity after incubation at 80 °C for 180 min, was achieved by adding 10 mM Ca2+ and 40 mM Na+ simultaneously. The increase in Bst-MFAse thermostability imparted by the addition of Ca2+ and Na+ may be associated with an important Ca2+–Na+–Ca2+ triad structure. This study provides an effective way to enhance the thermostability of Bst-MFAse and related enzymes.