Mapping the intestinal alpha-glucogenic enzyme specificities of starch digesting maltase-glucoamylase and sucrase-isomaltase Kyra Jones a , Lyann Sim b , Sankar Mohan c , Jayakanthan Kumarasamy c , Hui Liu c , Stephen Avery d , Hassan Y. Naim e , Roberto Quezada-Calvillo d,f , Buford L. Nichols d , B. Mario Pinto c , David R. Rose a,⇑ a Department of Biology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 b Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-1799 Copenhagen V, Denmark c Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 d USDA, Agricultural Research Service, Children’s Nutrition Research Center and Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030-300, USA e Department of Physiological Chemistry, University of Veterinary Medicine, Hannover, Germany f CIEP-Facultad de Ciencias Quimicas, Universidad Autonoma de San Luis Potosí, Zona Universitaria, San Luis Potosí, S.L.P. 78360, Mexico article info Article history: Received 21 March 2011 Revised 12 May 2011 Accepted 18 May 2011 Available online 24 May 2011 Keywords: Maltase-glucoamylase Sucrase-isomaltase Inhibition profiles Glucosidase inhibition abstract Inhibition of intestinal a-glucosidases and pancreatic a-amylases is an approach to controlling blood glu- cose and serum insulin levels in individuals with Type II diabetes. The two human intestinal glucosidases are maltase-glucoamylase and sucrase-isomaltase. Each incorporates two family 31 glycoside hydrolases responsible for the final step of starch hydrolysis. Here we compare the inhibition profiles of the individ- ual N- and C-terminal catalytic subunits of both glucosidases by clinical glucosidase inhibitors, acarbose and miglitol, and newly discovered glucosidase inhibitors from an Ayurvedic remedy used for the treat- ment of Type II diabetes. We show that features of the compounds introduce selectivity towards the sub- units. Together with structural data, the results enhance the understanding of the role of each catalytic subunit in starch digestion, helping to guide the development of new compounds with subunit specific antidiabetic activity. The results may also have relevance to other metabolic diseases such as obesity and cardiovascular disease. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Starch comprises a substantial portion of the human diet and plays an integral role in human metabolism, contributing a sizable fraction of total caloric intake. Starch is digested to glucose in the small intestine, contributing to the postprandial rise in blood glu- cose levels as well as insulin response. 1 Two macromolecules com- prise starch, amylose and amylopectin. Amylose is a linear chain polymer of a-D-glucopyranose units linked by a-1,4 bonds, with only minor branching. Amylopectin is a branched polymer of a- D-glucopyranose linked by a-1,4 linkages with branching a-1,6 bonds. The digestion of starch to glucose requires multiple enzymatic reactions in the human body. Glucose is only a minor product of a-amylase digestion of starch, the major products being soluble glucose oligomers, with both linear and branched structures. 2 The small, linear and branched a-limit oligomers (dextrins) pro- duced by a-amylase hydrolysis cannot be absorbed into the blood- stream and must be further hydrolyzed to free glucose. Maltase- glucoamylase (MGAM) and sucrose-isomaltase (SI) process the small linear oligomers and a-limit dextrins in the small intestine. 3 The apparent redundancy in glucosidase activities in the gut, as de- scribed below, is not understood and forms the basis for the pres- ent study. Here, we compare the kinetic effect on the four catalytic sub- units by six inhibitors: two of the currently available antidiabetic drugs, acarbose 4 (1) and miglitol 5 (2), a novel class of sulfonium- ion glucosidase inhibitors, salacinol (3), kotalanol (4), and de-O- sulfonated kotalanol (5), isolated from an Ayurvedic antidiabetic medicinal plant, Salacia reticulata, and the selenium analogue of salacinol, namely blintol (6)(Fig. 1). The results demonstrate cata- lytic domain selectivity, helping differentiate the active site requirements of each catalytic subunit. This directly enhances the understanding of the role these enzymes play in glucogenesis of starch in vivo. The future applications of this research include the ability to turn the enzyme activities on and off in animal mod- els individually and in various combinations and eventually mod- ulation of MGAM and SI activity as an effective method to control serum insulin and blood glucose levels. 2. Biology SI demonstrates hydrolytic activity on branched a-1,6 link- ages, which is complemented by the hydrolytic activity of both 0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2011.05.033 ⇑ Corresponding author. E-mail address: drrose@uwaterloo.ca (D.R. Rose). Bioorganic & Medicinal Chemistry 19 (2011) 3929–3934 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry journal homepage: www.elsevier.com/locate/bmc