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

Abstract

Genome of an early-diverged yeast <i>Blastobotrys</i> (<i>Arxula</i>) <i>adeninivorans</i> (<i>Ba</i>) encodes 88 glycoside hydrolases (GHs) including two α-glucosidases of GH13 family. One of those, the <i>rna_ARAD1D20130g</i>-encoded protein (<i>Ba</i>AG2; 581 aa) was overexpressed in <i>Escherichia coli</i>, 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 <i>Ba</i>AG2, whereas isomaltose and isomaltose-like substrates (palatinose, α-methylglucoside) were not, confirming that <i>Ba</i>AG2 is a maltase. <i>Ba</i>AG2 was competitively inhibited by a diabetes drug acarbose (K_i = 0.8 µM) and Tris (K_i = 70.5 µM). <i>Ba</i>AG2 was competitively inhibited also by isomaltose-like sugars and a hydrolysis product-glucose. At high maltose concentrations, <i>Ba</i>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. <i>Saccharomyces cerevisiae</i> maltase MAL62, studied for comparison, had only minimal ability to hydrolyze these polymers, and its transglycosylating activity was about three times lower compared to <i>Ba</i>AG2. Sequence identity of <i>Ba</i>AG2 with other maltases was only moderate being the highest (51%) with the maltase MalT of <i>Aspergillus oryzae</i>.