Binding of bivalent ions to actinomycete mannanase is accompanied by conformational change and is a key factor in its thermal stability

► We cloned and expressed the mannanases of Streptomyces thermoluteus and S. lividans. ► Carbohydrate-binding modules enhanced mannanase activity, but not thermal stability. ► Binding of certain bivalent ions to mannanase enhanced thermal stability. ► Binding involved positive entropy change due to dehydration of protein-bivalent ion. ► Conformational change induced by certain bivalent ions was different among mannanases.