Structure and evolution of the mammalian maltase-glucoamylase and sucrase-isomaltase genes

Maltase-glucoamylase and sucrase-isomaltase are two glycosydases responsible for starch digestion in human. Their evolutionary history was studied by comparing the amino acid sequences of these enzymes from several mammals and their orthologs from other chordates. The two glycosydases are paralogs and contain catalytic domains of the GH31 family. A common evolutionary precursor of their genes arose via a tandem duplication. As a consequence, sucrase-isomaltase consists of two homologous parts. The maltase-glucoamylase gene experienced several additional duplications, whose number varies among mammals. Its locus harbors four to seven tandem repeats, each coding for an amino acid sequence similar to the two parts of sucrase-isomaltase.