The Experts below are selected from a list of 1428 Experts worldwide ranked by ideXlab platform
Hassan Y. Naim - One of the best experts on this subject based on the ideXlab platform.
-
Differential Effects of Sucrase-Isomaltase Mutants on Its Trafficking and Function in Irritable Bowel Syndrome: Similarities to Congenital Sucrase-Isomaltase Deficiency.
Nutrients, 2020Co-Authors: Diab M. Husein, Sandra Rizk, Hassan Y. NaimAbstract:Congenital Sucrase-Isomaltase deficiency (CSID) is a rare metabolic intestinal disorder with reduced or absent activity levels of Sucrase-Isomaltase (SI). Interestingly, the main symptoms of CSID overlap with those in irritable bowel syndrome (IBS), a common functional gastrointestinal disorder with unknown etiology. Recent advances in genetic screening of IBS patients have revealed rare SI gene variants that are associated with IBS. Here, we investigated the biochemical, cellular and functional phenotypes of several of these variants. The data demonstrate that the SI mutants can be categorized into three groups including immature, mature but slowly transported, and finally mature and properly transported but with reduced enzymatic activity. We also identified SI mutant phenotypes that are deficient but generally not as severe as those characterized in CSID patients. The variable effects on the trafficking and function of the mutations analyzed in this study support the view that both CSID and IBS are heterogeneous disorders, the severity of which is likely related to the biochemical phenotypes of the SI mutants as well as the environment and diet of patients. Our study underlines the necessity to screen for SI mutations in IBS patients and to consider enzyme replacement therapy as an appropriate therapy as in CSID.
-
Heterozygotes Are a Potential New Entity among Homozygotes and Compound Heterozygotes in Congenital Sucrase-Isomaltase Deficiency
Nutrients, 2019Co-Authors: Diab M. Husein, Klauspeter Zimmer, Dalanda Wanes, Lara M. Marten, Hassan Y. NaimAbstract:Congenital Sucrase-Isomaltase deficiency (CSID) is an autosomal recessive disorder of carbohydrate maldigestion and malabsorption caused by mutations in the Sucrase-Isomaltase (SI) gene. SI, together with maltase-glucoamylase (MGAM), belongs to the enzyme family of disaccharidases required for breakdown of α-glycosidic linkages in the small intestine. The effects of homozygote and compound heterozygote inheritance trait of SI mutations in CSID patients have been well described in former studies. Here we propose the inclusion of heterozygote mutation carriers as a new entity in CSID, possibly presenting with milder symptoms. The hypothesis is supported by recent observations of heterozygote mutation carriers among patients suffering from CSID or patients diagnosed with functional gastrointestinal disorders. Recent studies implicate significant phenotypic heterogeneity depending on the character of the mutation and call for more research regarding the correlation of genetics, function at the cellular and molecular level and clinical presentation. The increased importance of SI gene variants in irritable bowel syndrome (IBS) or other functional gastrointestinal disorders FGIDs and their available symptom relief diets like fermentable oligo-, di-, mono-saccharides and polyols FODMAPs suggest that the heterozygote mutants may affect the disease development and treatment.
-
phylogenetic analysis reveals key residues in substrate hydrolysis in the Isomaltase domain of Sucrase Isomaltase and its role in starch digestion
Biochimica et Biophysica Acta, 2019Co-Authors: Marcia M Chaudet, Mahdi Amiri, Nathalie Marth, Hassan Y. NaimAbstract:Abstract Background Starch constitutes one of the main sources of nutrition in the human diet and is broken down through a number of stages of digestion. Small intestinal breakdown of starch-derived substrates occurs through the mechanisms of small intestinal brush border enzymes, maltase-glucoamylase and Sucrase-Isomaltase. These enzymes each contain two functional enzymatic domains, and though they share sequence and structural similarities due to their evolutionary conservation, they demonstrate distinct substrate preferences and catalytic efficiency. The N-terminal Isomaltase domain of Sucrase-Isomaltase has a unique ability to actively hydrolyze isomaltose substrates in contrast to the Sucrase, maltase and glucoamylase enzymes. Methods Through phylogenetic analysis, structural comparisons and mutagenesis, we were able to identify specific residues that play a role in the distinct substrate preference. Mutational analysis and comparison with wild-type activity provide evidence that this role is mediated in part by affecting interactions between the Sucrase and Isomaltase domains in the intact molecule. Results The sequence analysis revealed three residues proposed to play key roles in Isomaltase specificity. Mutational analysis provided evidence that these residues in Isomaltase can also affect activity in the partner Sucrase domain, suggesting a close interaction between the domains. Major conclusions The Sucrase and Isomaltase domains are closely interacting in the mature protein. The activity of each is affected by the presence of the other. General Significance: There has been little experimental evidence previously of the effects on activity of interactions between the Sucrase-Isomaltase enzyme domains. By extension, similar interactions might be expected in the other intestinal α-glucosidase, maltase-glucoamylase.
-
molecular pathogenicity of novel Sucrase Isomaltase mutations found in congenital Sucrase Isomaltase deficiency patients
Biochimica et Biophysica Acta, 2017Co-Authors: Birthe Gericke, Mahdi Amiri, Ronald C Scott, Hassan Y. NaimAbstract:Abstract Background & aims Congenital Sucrase-Isomaltase deficiency (CSID) is a genetic disorder associated with mutations in the Sucrase-Isomaltase ( SI ) gene. The diagnosis of congenital diarrheal disorders like CSID is difficult due to unspecific symptoms and usually requires invasive biopsy sampling of the intestine. Sequencing of the SI gene and molecular analysis of the resulting potentially pathogenic SI protein variants may facilitate a diagnosis in the future. This study aimed to categorize SI mutations based on their functional consequences. Methods cDNAs encoding 13 SI mutants were expressed in COS-1 cells. The molecular pathogenicity of the resulting SI mutants was defined by analyzing their biosynthesis, cellular localization, structure and enzymatic functions. Results Three biosynthetic phenotypes for the novel SI mutations were identified. The first biosynthetic phenotype was defined by mutants that are intracellularly transported in a fashion similar to wild type SI and with normal, but varying, levels of enzymatic activity. The second biosynthetic phenotype was defined by mutants with delayed maturation and trafficking kinetics and reduced activity. The third group of mutants is entirely transport incompetent and functionally inactive. Conclusions The current study unraveled CSID as a multifaceted malabsorption disorder that comprises three major classes of functional and trafficking mutants of SI and established a gradient of mild to severe functional deficits in the enzymatic functions of the enzyme. General significance This novel concept and the existence of mild consequences in a number of SI mutants strongly propose that CSID is an underdiagnosed and a more common intestinal disease than currently known.
-
The multiple roles of Sucrase-Isomaltase in the intestinal physiology
Molecular and Cellular Pediatrics, 2016Co-Authors: Birthe Gericke, Mahdi Amiri, Hassan Y. NaimAbstract:Osmotic diarrhea and abdominal pain in humans are oftentimes associated with carbohydrate malabsorption in the small intestine due to loss of function of microvillar disaccharidases. Disaccharidases are crucial for the digestion and the subsequent absorption of carbohydrates. This review focuses on Sucrase-Isomaltase as the most abundant intestinal disaccharidase and the primary or induced pathological conditions that affect its physiological function. Congenital defects are primary factors which directly influence the transport and function of Sucrase-Isomaltase in a healthy epithelium. Based on the mutation type and the pattern of inheritance, a mutation in the Sucrase - Isomaltase gene may exert a variety of symptoms ranging from mild to severe. However, structure and function of wild type Sucrase-Isomaltase can be also affected by secondary factors which influence its structure and function either specifically via certain inhibitors and therapeutic agents or generally as a part of intestinal pathogenesis, for example in the inflammatory responses. Diagnosis of Sucrase-Isomaltase deficiency and discriminating it from other gastrointestinal intolerances can be latent in the patients because of common symptoms observed in all of these cases. Here, we summarize the disorders that implicate the digestive function of Sucrase-Isomaltase as well as the diagnostic and therapeutic strategies utilized to restore normal intestinal function.
Buford L Nichols - One of the best experts on this subject based on the ideXlab platform.
-
phenolic compounds increase the transcription of mouse intestinal maltase glucoamylase and Sucrase Isomaltase
Food & Function, 2017Co-Authors: Meric Simsek, Roberto Quezadacalvillo, Buford L Nichols, Bruce R HamakerAbstract:Diverse natural phenolic compounds show inhibition activity of intestinal α-glucosidases, which may constitute the molecular basis for their ability to control systemic glycemia. Additionally, phenolics can modify mRNA expression for proteins involved in nutritional, metabolic or immune processes. To explore the possibility that phenolics can regulate the mRNA expression, enzymatic activity, and protein synthesis/processing of intestinal Maltase-Glucoamylase (MGAM) and Sucrase-Isomaltase (SI), small intestinal explants from Balb/c mice were cultured for 24 h in the presence or absence of gallic acid, caffeic acid, and (+)-catechin at 0.1, 0.5, and 1 mM. We measured the levels of MGAM and SI mRNA expression by qRT-PCR, maltase and Sucrase activities by a standard colorimetric method and the molecular size distribution of MGAM and SI proteins by western blotting. mRNA expression for MGAM was induced by the three phenolic compounds at 0.1 mM. mRNA expression for SI was induced by caffeic and gallic acids, but not by (+)-catechin. Caffeic acid was the most effective inducer of mRNA expression of these enzymes. Total maltase and Sucrase activities were not affected by treatment with phenolics. The proportion of high molecular size forms of MGAM was significantly increased by two of the three phenolic compounds, but little effect was observed on SI proteins. Thus, changes in the protein synthesis/processing, affecting the proportions of the different molecular forms of MGAM, may account for the lack of correlation between mRNA expression and enzymatic activity.
-
protein synthesis controls the activity of maltase glucoamylase and Sucrase Isomaltase in non intestinal tissues
The FASEB Journal, 2015Co-Authors: Meric Simsek, Roberto Quezadacalvillo, Jacquelin Juarez, Buford L NicholsAbstract:Maltase-Glucoamylase (MGAM) and Sucrase-Isomaltase (SI) are α-glucosidases of the membrane of small intestinal enterocytes responsible for the digestion of dietary carbohydrates into glucose and other monosaccharides. MGAM and SI mRNA expression, protein synthesis and catalytic activity of MGAM and SI are found predominantly in enterocytes; however, they are also found in lower amounts in other non-intestinal tissues, notably blood leukocytes and kidney cells. Little information exists on the functions, the mRNA expression, the nature of the respective proteins and catalytic properties of MGAM and SI in non-intestinal tissues. To correlate the transcription, synthesis and activity of these enzymes, we measured the mRNA expression of MGAM and SI; the catalytic activities of maltase, Sucrase, and Isomaltase; and the presence of the respective proteins in small intestine and other tissues such as spleen, kidney and pancreas of 8 weeks old mice. Small intestine showed the highest level of mRNA expression of M...
-
inhibition of individual subunits of maltase glucoamylase and Sucrase Isomaltase by polyphenols 1045 26
The FASEB Journal, 2014Co-Authors: Meric Simsek, Roberto Quezadacalvillo, Buford L Nichols, Bruce R HamakerAbstract:Some polyphenols inhibit the activities of the four subunits of intestinal α-glucosidases, maltase-glucoamylase (Mgam) and Sucrase-Isomaltase (Si). The use of polyphenols as modulators of the rate ...
-
slower in vivo glucogenesis from starch oligomers by mucosal Sucrase Isomaltase 1039 8
The FASEB Journal, 2014Co-Authors: Amy Huimei Lin, Stephen E Avery, Roberto Quezadacalvillo, Bruce R Hamaker, Maricela Diazsotomayor, Shaji K Chacko, Anbuhkani Muniandy, Like Yan, Buford L NicholsAbstract:While luminal α-Amylase (AMY) is recognized as a starch digesting enzyme, the products require that glucose be hydrolyzed from the non-reducing ends of the oligosaccharide produced. Two mucosal enzyme complexes are required for glucogenesis: Maltase-glucoamylase (Mgam) is a fast and Sucrase-Isomaltase (Si) is a slow α-glucosidase. Mgam was knocked-out in mice with the objective of determining role of Si on in vivo starch digestion to glucose. 8 mice were fed 0.5 gm. of chow containing normal maize starch. 2 h after feeding they were euthanized and 4 segments of small bowel (SB) snap-frozen. The segments were thawed and homogenized in water. Protein assays were by Bradford method. The homogenate was denatured in 80% ethanol at 80°C. Supernatant was collected by centrifugation. Free glucose of concentrated supernatant was determined by glucose oxidase/peroxidase. Soluble oligosaccharides were determined by diluting supernatant with buffer, pH 4.5, in 10% ethanol and 2.5 units of amyloglucosidase (AMG) added...
-
maltase glucoamylase modulates gluconeogenesis and Sucrase Isomaltase dominates starch digestion glucogenesis
Journal of Pediatric Gastroenterology and Nutrition, 2013Co-Authors: Maricela Diazsotomayor, Stephen E Avery, Roberto Quezadacalvillo, Bruce R Hamaker, Shaji K Chacko, Zihua Ao, Buford L NicholsAbstract:OBJECTIVES: Six enzyme activities are needed to digest starch to absorbable free glucose; 2 luminal α-amylases (AMY) and 4 mucosal maltase-glucoamylase (MGAM) and Sucrase-Isomaltase (SI) subunit activities are involved in the digestion. The AMY activities break down starch to soluble oligomeric dextrins; mucosal MGAM and SI can either directly digest starch to glucose or convert the post-α-amylolytic dextrins to glucose. We hypothesized that MGAM, with higher maltase than SI, drives digestion on ad limitum intakes and SI, with lower activity but more abundant amount, constrains ad libitum starch digestion. METHODS: Mgam null and wild-type (WT) mice were fed with starch diets ad libitum and ad limitum. Fractional glucogenesis (fGG) derived from starch was measured and fractional gluconeogenesis and glycogenolysis were calculated. Carbohydrates in small intestine were determined. RESULTS: After ad libitum meals, null and WT had similar increases of blood glucose concentration. At low intakes, null mice had less (f)GG (P = 0.02) than WT mice, demonstrating the role of Mgam activity in ad limitum feeding; null mice did not reduce fGG responses to ad libitum intakes demonstrating the dominant role of SI activity during full feeding. Although fGG was rising after feeding, fractional gluconeogenesis fell, especially for null mice. CONCLUSIONS: The fGNG (endogenous glucogenesis) in null mice complemented the fGG (exogenous glucogenesis) to conserve prandial blood glucose concentrations. The hypotheses that Mgam contributes a high-efficiency activity on ad limitum intakes and SI dominates on ad libitum starch digestion were confirmed.
Roberto Quezadacalvillo - One of the best experts on this subject based on the ideXlab platform.
-
phenolic compounds increase the transcription of mouse intestinal maltase glucoamylase and Sucrase Isomaltase
Food & Function, 2017Co-Authors: Meric Simsek, Roberto Quezadacalvillo, Buford L Nichols, Bruce R HamakerAbstract:Diverse natural phenolic compounds show inhibition activity of intestinal α-glucosidases, which may constitute the molecular basis for their ability to control systemic glycemia. Additionally, phenolics can modify mRNA expression for proteins involved in nutritional, metabolic or immune processes. To explore the possibility that phenolics can regulate the mRNA expression, enzymatic activity, and protein synthesis/processing of intestinal Maltase-Glucoamylase (MGAM) and Sucrase-Isomaltase (SI), small intestinal explants from Balb/c mice were cultured for 24 h in the presence or absence of gallic acid, caffeic acid, and (+)-catechin at 0.1, 0.5, and 1 mM. We measured the levels of MGAM and SI mRNA expression by qRT-PCR, maltase and Sucrase activities by a standard colorimetric method and the molecular size distribution of MGAM and SI proteins by western blotting. mRNA expression for MGAM was induced by the three phenolic compounds at 0.1 mM. mRNA expression for SI was induced by caffeic and gallic acids, but not by (+)-catechin. Caffeic acid was the most effective inducer of mRNA expression of these enzymes. Total maltase and Sucrase activities were not affected by treatment with phenolics. The proportion of high molecular size forms of MGAM was significantly increased by two of the three phenolic compounds, but little effect was observed on SI proteins. Thus, changes in the protein synthesis/processing, affecting the proportions of the different molecular forms of MGAM, may account for the lack of correlation between mRNA expression and enzymatic activity.
-
protein synthesis controls the activity of maltase glucoamylase and Sucrase Isomaltase in non intestinal tissues
The FASEB Journal, 2015Co-Authors: Meric Simsek, Roberto Quezadacalvillo, Jacquelin Juarez, Buford L NicholsAbstract:Maltase-Glucoamylase (MGAM) and Sucrase-Isomaltase (SI) are α-glucosidases of the membrane of small intestinal enterocytes responsible for the digestion of dietary carbohydrates into glucose and other monosaccharides. MGAM and SI mRNA expression, protein synthesis and catalytic activity of MGAM and SI are found predominantly in enterocytes; however, they are also found in lower amounts in other non-intestinal tissues, notably blood leukocytes and kidney cells. Little information exists on the functions, the mRNA expression, the nature of the respective proteins and catalytic properties of MGAM and SI in non-intestinal tissues. To correlate the transcription, synthesis and activity of these enzymes, we measured the mRNA expression of MGAM and SI; the catalytic activities of maltase, Sucrase, and Isomaltase; and the presence of the respective proteins in small intestine and other tissues such as spleen, kidney and pancreas of 8 weeks old mice. Small intestine showed the highest level of mRNA expression of M...
-
inhibition of individual subunits of maltase glucoamylase and Sucrase Isomaltase by polyphenols 1045 26
The FASEB Journal, 2014Co-Authors: Meric Simsek, Roberto Quezadacalvillo, Buford L Nichols, Bruce R HamakerAbstract:Some polyphenols inhibit the activities of the four subunits of intestinal α-glucosidases, maltase-glucoamylase (Mgam) and Sucrase-Isomaltase (Si). The use of polyphenols as modulators of the rate ...
-
slower in vivo glucogenesis from starch oligomers by mucosal Sucrase Isomaltase 1039 8
The FASEB Journal, 2014Co-Authors: Amy Huimei Lin, Stephen E Avery, Roberto Quezadacalvillo, Bruce R Hamaker, Maricela Diazsotomayor, Shaji K Chacko, Anbuhkani Muniandy, Like Yan, Buford L NicholsAbstract:While luminal α-Amylase (AMY) is recognized as a starch digesting enzyme, the products require that glucose be hydrolyzed from the non-reducing ends of the oligosaccharide produced. Two mucosal enzyme complexes are required for glucogenesis: Maltase-glucoamylase (Mgam) is a fast and Sucrase-Isomaltase (Si) is a slow α-glucosidase. Mgam was knocked-out in mice with the objective of determining role of Si on in vivo starch digestion to glucose. 8 mice were fed 0.5 gm. of chow containing normal maize starch. 2 h after feeding they were euthanized and 4 segments of small bowel (SB) snap-frozen. The segments were thawed and homogenized in water. Protein assays were by Bradford method. The homogenate was denatured in 80% ethanol at 80°C. Supernatant was collected by centrifugation. Free glucose of concentrated supernatant was determined by glucose oxidase/peroxidase. Soluble oligosaccharides were determined by diluting supernatant with buffer, pH 4.5, in 10% ethanol and 2.5 units of amyloglucosidase (AMG) added...
-
maltase glucoamylase modulates gluconeogenesis and Sucrase Isomaltase dominates starch digestion glucogenesis
Journal of Pediatric Gastroenterology and Nutrition, 2013Co-Authors: Maricela Diazsotomayor, Stephen E Avery, Roberto Quezadacalvillo, Bruce R Hamaker, Shaji K Chacko, Zihua Ao, Buford L NicholsAbstract:OBJECTIVES: Six enzyme activities are needed to digest starch to absorbable free glucose; 2 luminal α-amylases (AMY) and 4 mucosal maltase-glucoamylase (MGAM) and Sucrase-Isomaltase (SI) subunit activities are involved in the digestion. The AMY activities break down starch to soluble oligomeric dextrins; mucosal MGAM and SI can either directly digest starch to glucose or convert the post-α-amylolytic dextrins to glucose. We hypothesized that MGAM, with higher maltase than SI, drives digestion on ad limitum intakes and SI, with lower activity but more abundant amount, constrains ad libitum starch digestion. METHODS: Mgam null and wild-type (WT) mice were fed with starch diets ad libitum and ad limitum. Fractional glucogenesis (fGG) derived from starch was measured and fractional gluconeogenesis and glycogenolysis were calculated. Carbohydrates in small intestine were determined. RESULTS: After ad libitum meals, null and WT had similar increases of blood glucose concentration. At low intakes, null mice had less (f)GG (P = 0.02) than WT mice, demonstrating the role of Mgam activity in ad limitum feeding; null mice did not reduce fGG responses to ad libitum intakes demonstrating the dominant role of SI activity during full feeding. Although fGG was rising after feeding, fractional gluconeogenesis fell, especially for null mice. CONCLUSIONS: The fGNG (endogenous glucogenesis) in null mice complemented the fGG (exogenous glucogenesis) to conserve prandial blood glucose concentrations. The hypotheses that Mgam contributes a high-efficiency activity on ad limitum intakes and SI dominates on ad libitum starch digestion were confirmed.
Erwin E. Sterchi - One of the best experts on this subject based on the ideXlab platform.
-
the maltase glucoamylase gene common ancestry to Sucrase Isomaltase with complementary starch digestion activities
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Buford L Nichols, Dagmar Hahn, Stephen E Avery, Dallas M. Swallow, Partha Sen, Erwin E. SterchiAbstract:Brush-border maltase-glucoamylase (MGA) activity serves as the final step of small intestinal digestion of linear regions of dietary starch to glucose. Brush-border Sucrase-Isomaltase (SI) activity is complementary, through digestion of branched starch linkages. Here we report the cloning and sequencing of human MGA gene and demonstrate its close evolutionary relationship to SI. The gene is approximately 82,000 bp long and located at chromosome 7q34. Forty-eight exons were identified. The 5' gene product, when expressed as the N-terminal protein sequence, hydrolyzes maltose and starch, but not sucrose, and is thus distinct from SI. The catalytic residue was identified by mutation of an aspartic acid and was found to be identical with that described for SI. The exon structures of MGA and SI were identical. This homology of genomic structure is even more impressive than the previously reported 59% amino acid sequence identity. The shared exon structures and peptide domains, including proton donors, suggest that MGA and SI evolved by duplication of an ancestral gene, which itself had already undergone tandem gene duplication. The complementary human enzyme activities allow digestion of the starches of plant origin that make up two-thirds of most diets.
-
the maltase glucoamylase gene common ancestry to Sucrase Isomaltase with complementary starch digestion activities
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Buford L Nichols, Dagmar Hahn, Stephen E Avery, Dallas M. Swallow, Erwin E. SterchiAbstract:Brush-border maltase-glucoamylase (MGA) activity serves as the final step of small intestinal digestion of linear regions of dietary starch to glucose. Brush-border Sucrase-Isomaltase (SI) activity is complementary, through digestion of branched starch linkages. Here we report the cloning and sequencing of human MGA gene and demonstrate its close evolutionary relationship to SI. The gene is ≈82,000 bp long and located at chromosome 7q34. Forty-eight exons were identified. The 5′ gene product, when expressed as the N-terminal protein sequence, hydrolyzes maltose and starch, but not sucrose, and is thus distinct from SI. The catalytic residue was identified by mutation of an aspartic acid and was found to be identical with that described for SI. The exon structures of MGA and SI were identical. This homology of genomic structure is even more impressive than the previously reported 59% amino acid sequence identity. The shared exon structures and peptide domains, including proton donors, suggest that MGA and SI evolved by duplication of an ancestral gene, which itself had already undergone tandem gene duplication. The complementary human enzyme activities allow digestion of the starches of plant origin that make up two-thirds of most diets.
-
human small intestinal maltase glucoamylase cdna cloning homology to Sucrase Isomaltase
Journal of Biological Chemistry, 1998Co-Authors: Buford L Nichols, Andrea Quaroni, Joyce A Eldering, Dagmar Hahn, Stephen E Avery, Erwin E. SterchiAbstract:Abstract It has been hypothesized that human mucosal glucoamylase (EC 3.2.1.20 and 3.2.1.3) activity serves as an alternate pathway for starch digestion when luminal α-amylase activity is reduced because of immaturity or malnutrition and that maltase-glucoamylase plays a unique role in the digestion of malted dietary oligosaccharides used in food manufacturing. As a first step toward the testing of this hypothesis, we have cloned human small intestinal maltase-glucoamylase cDNA to permit study of the individual catalytic and binding sites for maltose and starch enzyme hydrolase activities in subsequent expression experiments. Human maltase-glucoamylase was purified by immunoisolation and partially sequenced. Maltase-glucoamylase cDNA was amplified from human intestinal RNA using degenerate and gene-specific primers with the reverse transcription-polymerase chain reaction. The 6,513-base pair cDNA contains an open reading frame that encodes a 1,857-amino acid protein (molecular mass 209,702 Da). Maltase-glucoamylase has two catalytic sites identical to those of Sucrase-Isomaltase, but the proteins are only 59% homologous. Both are members of glycosyl hydrolase family 31, which has a variety of substrate specificities. Our findings suggest that divergences in the carbohydrate binding sequences must determine the substrate specificities for the four different enzyme activities that share a conserved catalytic site.
Peter G Traber - One of the best experts on this subject based on the ideXlab platform.
-
Sucrase Isomaltase gene expression in barrett s esophagus and adenocarcinoma
Gastroenterology, 1993Co-Authors: David G Beer, Jason H Moore, Mark B Orringer, Henry D Appelman, Peter G TraberAbstract:Abstract Background: Specialized Barrett's esophageal mucosa, characterized by incomplete intestinal metaplasia of the esophageal mucosa, is associated with the development of adenocarcinoma. Although the intestinal disaccharidase Sucrase-Isomaltase (SI) has been shown in incomplete intestinal metaplasia of the stomach, it is commonly believed that Barrett's mucosa does not express SI based on the lack of enzymatic activity. This study was undertaken to determine whether the SI gene is expressed in Barrett's epithelium and its associated adenocarcinoma at the level of messenger RNA (mRNA) and protein. Methods: Reverse transcription polymerase chain reaction was used to determine the presence of SI mRNA in Barrett's esophagus and esophageal adenocarcinomas. Cellular localization of SI protein was determined by immunohistochemistry. Results: SI mRNA was identified in 76% of Barrett's epithelium and 82% of esophageal adenocarcinomas. The transcriptional initiation site for SI in these tissues was identical to that of the small intestine. Immunohistochemical localization showed that SI was directed to the apical membrane in Barrett's epithelium in contrast to a more diffuse cytoplasmic pattern in esophageal adenocarcinomas. Conclusions: Columnar cells of specialized Barrett's epithelium express SI and are, therefore, phenotypically similar to those in incomplete intestinal metaplasia of the stomach with respect to intestinal gene expression.
-
the human Sucrase Isomaltase gene directs complex patterns of gene expression in transgenic mice
American Journal of Physiology-gastrointestinal and Liver Physiology, 1993Co-Authors: A J Markowitz, E H Birkenmeier, Peter G TraberAbstract:Sucrase-Isomaltase (SI) is an enterocyte-specific gene that is expressed in complex developmental and spatial patterns. In this study, we examine the ability of regulatory elements within the human...
-
novel dna binding proteins regulate intestine specific transcription of the Sucrase Isomaltase gene
Molecular and Cellular Biology, 1992Co-Authors: Peter G Traber, W WangAbstract:Sucrase-Isomaltase (SI) is an enterocyte-specific gene which exhibits a complex pattern of expression during intestinal development and in the adult intestinal mucosa. In the studies described in this report, we demonstrate that enterocyte-specific transcription of the SI gene is regulated by an evolutionarily conserved promoter that extends approximately 180 bp upstream of the transcription start site. DNase I footprint analysis allowed the identification of three nuclear protein-binding sites within the SI promoter (SIF1, SIF2, and SIF3 [SI footprint]), each of which acted as a positive regulatory element for transcription in intestinal cell lines. SIF1 was shown to bind nuclear protein complexes present in primary mouse small intestinal cell and in an intestinal cell line (Caco-2). However, SIF1-binding proteins were absent in a variety of other epithelial and nonepithelial cells. In vitro mutagenesis experiments demonstrated that the SIF1 site is required for high-level promoter activity in intestinal cells. The SIF3 element formed prominent binding complexes with intestinal and liver nuclear extracts, whereas nuclear proteins from other epithelial and nonepithelial cells formed weaker complexes of different mobilities. The SIF2 element bound nuclear proteins in a pattern similar to that of SIF3, and cross-competition studies suggested that SIF2 and SIF3 may bind the same nuclear proteins. Taken together, these data have allowed the identification of novel DNA-binding proteins that play an important role in regulating intestine-specific transcription of the SI gene.
-
isolation and characterization of the human Sucrase Isomaltase gene and demonstration of intestine specific transcriptional elements
Journal of Biological Chemistry, 1992Co-Authors: Wei Wang, Peter G TraberAbstract:Abstract The molecular mechanisms that regulate intestine-specific gene expression and the transition from proliferating, undifferentiated crypt cells to nonproliferating, differentiated villus cells are unknown. Sucrase-Isomaltase is an apical membrane disaccharidase that is found exclusively in enterocytes of adult intestine and is expressed in a complex pattern along the intestinal crypt-villus axis. To investigate the regulation of Sucrase-Isomaltase, we have cloned and sequenced 3.6 kilobases of the 5'-flanking region of the human Sucrase-Isomaltase gene. The transcriptional start site was mapped in human small intestine and in a colonic adenocarcinoma cell line (Caco-2) using an anchored polymerase chain reaction, primer extension, and RNase protection assays. The 5'-flanking DNA of the gene was linked to either chloramphenicol acetyltransferase or luciferase reporter genes and used for transfection into Caco-2, HeLa, and HepG2 cells. This analysis demonstrated that intestine-specific transcription of the Sucrase-Isomaltase gene involves both proximal and distal regulatory elements. Use of Sucrase-Isomaltase as a model gene will allow investigation of the mechanisms that regulate transcription of enterocyte-specific genes, developmental gene expression in the small intestine and colon, and the process of differentiation as epithelial cells migrate from intestinal crypts onto the villus in adult intestine.
