Human small intestinal maltase-glucoamylase cDNA cloning. Homology to sucrase-isomaltase.
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 alpha-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.
Nichols
B L
BL
United States Department of Agriculture Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-2600, USA.
Eldering
J
J
Avery
S
S
Hahn
D
D
Quaroni
A
A
Sterchi
E
E
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003001:Cloning, Molecular; D016384:Consensus Sequence; D018076:DNA, Complementary; D004926:Escherichia coli / Q000235:genetics; D000882:Haplorhini; D006801:Humans; D007421:Intestine, Small / Q000201:enzymology*; D051379:Mice; D008969:Molecular Sequence Data; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis; D013045:Species Specificity; D013379:Substrate Specificity; D014018:Tissue Distribution; D000520:alpha-Glucosidases / Q000235:genetics*
D018076:DNA, Complementary; D011994:Recombinant Proteins; D000520:alpha-Glucosidases