The maltase-glucoamylase gene: Common ancestry to sucrase-isomaltase with complementary starch digestion activities

Buford L. Nichols*, Stephen Avery, Partha Sen, Dallas M. Swallow, Dagmar Hahn, Erwin Sterchi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

122 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1432-1437
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume100
Issue number3
DOIs
StatePublished - Feb 4 2003

Keywords

  • Family 31 glucoside hydrolases
  • Granulocyte
  • Small intestine

ASJC Scopus subject areas

  • General

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