Allosteric properties of Geobacillus maltogenic amylase.

Maltogenic amylases (MAases, EC 3.2.1.133) have been gotten much attention due to their various applications in industry and commercial processes. MAases belong to subfamily 20 of glycoside hydrolase family 13 (NPase or CDases subfamily) and they have important differences with other members of the family. This enzyme consists of two subunits which form two active sites in the dimer form by binding of the central domain of each subunit to the N domain of the next one (domain-swapping dimeric structure). Allosterism is a possible way of regulating enzymatic activity and no evidence has been found regarding to the cooperativity and correlation between MAases subunits, therefore in this study the allosteric behavior of MAases from a native strain (Geobacillus sp. Gh6) was investigated. Unlike other members of α-amylase family, MAases showed positive cooperativity between their subunits and the enzyme exhibited sigmoidal nature towards all three cyclodextrin (CD) substrates with a Hill constant (nH) value equal to 2, 1.6 and 1.1 for α-CD, β-CD and γ-CD, respectively. On further analysis, the effect of glucose and maltose as MAases allosteric effectors in the presence of β-CD substrate showed that these two effectors had a biphasic effect; while they stimulated the enzyme activity at low concentrations (with a decrease in Hill constant), these metabolites acted as allosteric inhibitors at higher concentrations. Due to the key role of MAases in carbohydrate metabolization, an efficient regulating system for this enzyme is required. In this experiment, for the first time the allosteric properties of MAases were observed and investigated.