Human maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) are the small-intestinal glucosidases responsible for catalyzing the last glucose-releasing step in starch digestion. MGAM and SI are each composed of duplicated catalytic domains, N- and C-terminal, which display complementary substrate specificities for the mixture of short linear and branch oligosaccharide substrates that typically make up terminal starch digestion products. As MGAM and SI are involved in post-prandial glucose production, regulating their activities with α-glucosidase inhibitors is an attractive approach to controlling blood glucose levels for the prevention and treatment of Type 2 diabetes. To better understand the complementary activities and mechanism of inhibition of these intestinal glucosidases, this thesis aims to characterize the individual N- and C-terminal MGAM and SI domains using a combination of X-ray crystallographic structural studies, enzyme kinetics, and inhibitor studies. First, the structure of the N-terminal domain of MGAM (ntMGAM) was determined in its apo form and in complex with the inhibitor acarbose. In addition to sequence alignments and kinetics studies, the structures provide insight into the preference of the N-terminal MGAM domain for short linear substrates and the C-terminal domain for longer substrates. Second, the structure of ntMGAM was determined in complex with various α-glucosidase inhibitors, including those currently on the market (acarbose and miglitol), a new class of inhibitors from natural extracts of Salacia reticulata (salacinol, kotalanol and de-O-sulfonated kotalanol) and chemically synthesized derivatives of salacinol. These studies reveal the features of the Salacia reticulata inhibitors that are essential for inhibitory activity and highlight their potential as future drug candidates. Third, the crystal structure of the N-terminal domain of SI (ntSI) was determined in apo-form and in complex with kotalanol. Structural comparison of ntSI and ntMGAM reveal key differences in active site architectures, which are proposed to confer differential substrate specificity.

Human maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) are the small-intestinal glucosidases responsible for catalyzing the last glucose-releasing step in starch digestion. MGAM and SI are each composed of duplicated catalytic domains, N- and C-terminal, which display complementary substrate specificities for the mixture of short linear and branch oligosaccharide substrates that typically make up terminal starch digestion products. As MGAM and SI are involved in post-prandial glucose production, regulating their activities with α-glucosidase inhibitors is an attractive approach to controlling blood glucose levels for the prevention and treatment of Type 2 diabetes. To better understand the complementary activities and mechanism of inhibition of these intestinal glucosidases, this thesis aims to characterize the individual N- and C-terminal MGAM and SI domains using a combination of X-ray crystallographic structural studies, enzyme kinetics, and inhibitor studies. First, the structure of the N-terminal domain of MGAM (ntMGAM) was determined in its apo form and in complex with the inhibitor acarbose. In addition to sequence alignments and kinetics studies, the structures provide insight into the preference of the N-terminal MGAM domain for short linear substrates and the C-terminal domain for longer substrates. Second, the structure of ntMGAM was determined in complex with various α-glucosidase inhibitors, including those currently on the market (acarbose and miglitol), a new class of inhibitors from natural extracts of Salacia reticulata (salacinol, kotalanol and de-O-sulfonated kotalanol) and chemically synthesized derivatives of salacinol. These studies reveal the features of the Salacia reticulata inhibitors that are essential for inhibitory activity and highlight their potential as future drug candidates. Third, the crystal structure of the N-terminal domain of SI (ntSI) was determined in apo-form and in complex with kotalanol. Structural comparison of ntSI and ntMGAM reveal key differences in active site architectures, which are proposed to confer differential substrate specificity.