Evolution of intestinal α-glucosidases in vertebrates: Genomic and proteomic data upend previous hypotheses

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

Tampa Florida

Congreso; SICB Annual Meeting; 2019

Society for Integrative and Comparative Biology

Researchers have presumed that 2 distinct enzymes, orthologs ofmammalian sucrase-isomaltase (SI) and maltase-glucoamylase(MGAM), are responsible for sucrasic and maltasic activities invertebrates. Using phylogenetic analyses on genomic data andenzymatic assays, we uncovered a single ancestral „-glucosidase(AG) gene (which we here call AAG), homologous to the oneprimarily annotated as SI in available genomes. AAG appears to bewidespread among vertebrates and to have given rise to additionalAG genes in mammals and some birds: the enzyme called MGAM isnot shared by all vertebrates, but is specific to mammals. Themajority of Passeriformes (a group including almost half of all birds)appear to have only AAG and its product has both maltasic andsucrasic activity. The existence of many granivorous songbirdspecies indicates that the presence of two AGs is not a necessarycondition for reliance on starchy food. Proteomic and biochemicalassays in isolated brush border membrane (bbm) of 3 songbirds andchickens demonstrate that songbirds express a single enzyme butchickens have a duplicated AG present in the bbm, as predicted bygenomic data. Data also revealed that birds in a large songbird clade,the starlings and relatives, lack sucrasic activity because their AAGgene has undergone a functional shift, and lost sucrasic but retainedmaltasic activity. Our findings suggest greater diversity and differentevolutionary history of bbm AGs than previously presumed, withwidespread implications for our understanding of the digestivephysiology of the majority of vertebrates. Supported by NSFIOS-1354893