Ct‐MGAM Activity Adapts to Various Botanical Food Starch Intakes by Alternative Splicing

Abstract

Maltase‐Glucoamylase (MGAM) is one of the intestinal mucosal α‐glucosidases responsible for the final digestion of starch to free glucose. In humans membrane‐bound MGAM is formed by two subunits: a N‐terminal (Nt‐MGAM) subunit with slow activity against αamylase pretreated α‐Limit Dextrins (α‐LDx); and a C‐terminal (Ct‐MGAM) subunit with fast activity against α‐LDx and substrate inhibition by the shortest glucans. In mammals, including humans, the 3′‐region of the MGAM gene coding the Ct subunit contains from 4 to 6 paralogous copies, each for a varied subunit. Although expression of mRNA from these copies has been observed, the biological significance of the variable 3′ Ct regions undocumented. Here we report 4 different mRNAs coding for Ct‐MGAM, each by alternative splicing. The recombinant expression of these 4 subunits produced active enzymes with differences in their kinetic properties of catalysis. These observations indicate that variable Ct‐MGAM subunits are the result of alternative splicing arising from paralogous duplications in the MGAM gene's 3′‐region. The resulting “splicoform” Ct‐MGSM enzymes may be a mechanism for efficient digestion of glucans with variable α‐LDx structures generated by αamylase from starches of different botanical origin. Supported by CNRC/ARS/USDA and CONACYT‐Mexico.