Evolution and function of the key digestive enzymes sucrase and maltase in vertebrates

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

Turku

Congreso; ESEB Biennial Congess; 2019

The European Society for Evolutionary Biology

Diets vary greatly across species, and consequently, digestive systems exhibit great morphological and enzymatic diversity, since extracting sufficient energy from food sources is critical for survival. In many vertebrates, a main source of energy is carbohydrates. Hexose monomers such as glucose and fructose can be readily absorbed and transported in blood, while disaccharides, such as sucrose and maltose, need to be broken into their constituent hexoses before being absorbed. Mammals digest these disaccharides using the enzymes sucrase-isomaltase (SI) and maltase-glucoamylase (MGAM). Maltose can be hydrolyzed by both SI and MGAM, while sucrose is hydrolyzed by SI. This dual-enzyme model has been assumed to be ancestral in vertebrates, given the presence of two enzymes with similar characteristics in mammals and some birds. Through genomic and phylogenetic analyses we discovered, unexpectedly, that this is not the case: the ancestral state of vertebrates is a digestive system with a single disaccharidase, orthologous to the mammalian SI, with independent duplications in mammals (resulting in MGAM) and birds (resulting in a new enzyme, which we call ADAG). In addition, we developed a cell based assay to test the function of these enzymes. We discovered that the human and chicken SI share functional similarities and that surprisingly, the avian duplicate has converged in function with the mammalian maltase, exhibiting a higher activity against maltose than sucrose. Our findings reveal a previously unexplored diversity in disaccharidase repertoire and function across vertebrates, with major implications for the evolution of diet selection and ecological niche.