New insights from genomics and proteomics in vertebrate intestinal carbohydrate digestion

ANTONIO BRUN; MENDEZ-ARANDA, DANIEL; MAGALLANES, MELISA; KARASOV WH; MARTINEZ DEL RIO, CARLOS; BALDWIN, MAUDE; CAVIEDES-VIDAL E

Sevilla

Congreso; Annual Meeting SEB; 2019

Society for Experimental Biology

Present knowledge presumes that in vertebrates, the enzymes sucrase-isomaltase (SI) and maltase-glucoamylase (MGAM) are responsible for the digestion oligo- and disaccharides (e.g., maltose, sucrose, etc.) at the small intestine apical membrane. Such knowledge has its origin in mammalian studies where those two orthologs perform these functions. We tested if this hydrolytic system is conserved within all vertebrates by searching databases for SI and MGAM sequences. Surprisingly, we found that only SI was common to all clades and just some (all mammals, some fishes and birds) exhibited both sequences. Phylogenetic inference revealed the ancestral condition of SI and that MGAM appeared in different evolutionary events along clades. We tested this finding using zymography coupled to proteomics assaying brush-border membrane of rats, mice, chickens, zebra finches and house sparrows. In the first three species our genomic study produced sequences of SI and a maltase-glucoamylase, while in the passerine species, only SI was found. Maltose, sucrose and isomaltose were used as substrates for the zymography. Glucose assay on the zymography gels produced bands in all species? lanes revealing alpha-glucosidase enzyme activity. These bands were cut and assayed for proteins. Proteomics confirmed our genomics findings: SI and a maltase-glucoamylase were responsible for the hydrolysis in mammals and chickens and only one enzyme, SI, accounted for all alpha-glucosidase activity in passerines. Findings suggest greater diversity and different evolutionary history of the brush-border membrane alpha-glucosidases than previously presumed, with widespread implications for our understanding of the digestive physiology of the majority of vertebrates. Supported by NSF-IOS1354893.