Characterization of a Maltase from an Early-Diverged Non-Conventional Yeast .

Genome of an early-diverged yeast () () encodes 88 glycoside hydrolases (GHs) including two α-glucosidases of GH13 family. One of those, the -encoded protein (AG2; 581 aa) was overexpressed in , purified and characterized. We showed that maltose, other maltose-like substrates (maltulose, turanose, maltotriose, melezitose, malto-oligosaccharides of DP 4‒7) and sucrose were hydrolyzed by AG2, whereas isomaltose and isomaltose-like substrates (palatinose, α-methylglucoside) were not, confirming that AG2 is a maltase. AG2 was competitively inhibited by a diabetes drug acarbose (K = 0.8 µM) and Tris (K = 70.5 µM). AG2 was competitively inhibited also by isomaltose-like sugars and a hydrolysis product-glucose. At high maltose concentrations, AG2 exhibited transglycosylating ability producing potentially prebiotic di- and trisaccharides. Atypically for yeast maltases, a low but clearly recordable exo-hydrolytic activity on amylose, amylopectin and glycogen was detected. maltase MAL62, studied for comparison, had only minimal ability to hydrolyze these polymers, and its transglycosylating activity was about three times lower compared to AG2. Sequence identity of AG2 with other maltases was only moderate being the highest (51%) with the maltase MalT of .