Dual-Activity Mannosyltransferase Phosphorylases in Family 130 of Glycoside Hydrolases

We discovered that certain mannoside-active enzymes from family GH130 possess both glycoside phosphorylase (GP) and weak glycosyltransferase (GT) activities. This dual activity was observed only in glycoside phosphorylases acting on β-(1,2)- and β-(1,3)-mannosides, being absent in β-(1,4)-mannoside phosphorylases. We provide several three-dimensional (3D) structures of β-(1,2)-mannosyltransferase phosphorylases Uhgb_MS (identified from the human gut microbiome (subfamily GH130_4)) and Teth514_1788 (from <i>Thermoanaerobacter</i> sp. X514 (subfamily GH130_6)) and analyzed GT/GP partitioning among enzymes acting on d-mannosides. Structural analysis and mutagenesis of Uhgb_MS allowed us to show that loop L2 folding, as well as nucleotide and phosphate binding residues (P206, N211, R242) at the location of the common structural phosphate of αMan1P and GDP-Man, is an important structural element of bifunctionality in GH130.