Many biologically active compounds are glycosylated metabolites. The functional contribution of sugars to biologically active compounds has been reviewed throughout different exciting compilations, in which have been highlighted that the sugar can determine biological activity, drug targeting and pharmacokinetics.[1,2] This fact offers interesting biological applications, since the modification of the sugar, or the type of glycosidic linkage, could allow the improvement of desired stability properties. Regarding this, the C-C glycosidic linkage is metabolically more stable than the C-O, due to its resistance against glycosidase degradation or hydrolysis.  Thus, pioneering studies of the enzymes that are able to catalyze the formation of C-C and C-O glycosidic bonds gain special importance in the development of more effective antibiotics. Glycosylation reactions are catalyzed by Glycosyltransferases (GTs), which use an activated sugar donor substrate for transferring a wide array of glycosyl moieties onto the nucleophilic group of sugars and other kind of organic molecules (acceptor substrate). GTs can invert or retain the anomeric configuration of the sugar that is being transferred and therefore, they are classified as inverting- or retaining-GTs, respectively.  So far, the lack of C-GTs crystal structures, which are enzymes that catalyze the formation of C-C glycosidic bonds, had hindered detailed studies of this type of sugar transfer reaction. The recent elucidation of both the O-GT LanGT2 (O-LanGT2) and its variant with C-glycosylation activity (C-LanGT2),  represents an encouraging opportunity to computational investigate the structural features that could cause the formation of the O- and the C-glycosylated product through the reaction catalyzed by O- and C-LanGT2, respectively. (Figure 1)
In the present study, ternary complex models were built and equilibrated for O- and C-LanGT2 by combining a Docking methodology with Molecular Dynamics (MD) simulations. To carry out the Docking and the MD simulations, AutoDock and NAMD programs were used, respectively. All results indicate that the structural features that could modulate the orientation of the acceptor substrate (TET) at its binding pocket are associated with loops 8-13, 51-62 and 219-228. Within these loops, residues as S8/A8, A62/I62 and R220 in O-LanGT2/C-LanGT2, are key to orient TET in a suitable disposition with regard to the sugar and therefore, for the O- and the C-glycosylation reaction.
Finally, we propose for first time a molecular interpretation of the specificity change from O- to C-glycosidic bond, and thus we hope that these results could provide valuable clues to guide the transformation of any O-GT into a C-GT.
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- Härle, J.; Günther, S.; Lauinger, B.; Weber, M.; Kammerer, B.; Zechel, David L.; Luzhetskyy, A.; Bechthold, A., Rational Design of an Aryl-C-Glycoside Catalyst from a Natural Product O-Glycosyltransferase. Chem. Biol., 2011, 18, 520-530.
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- Tam, H. K.; Harle, J.; Gerhardt, S.; Rohr, J.; Wang, G.; Thorson, J. S.; Bigot, A.; Lutterbeck, M.; Seiche, W.; Breit, B.; Bechthold, A.; Einsle, O., Structural Characterization of O- and C-Glycosylating Variants of the Landomycin Glycosyltransferase LanGT2. Angew. Chem. Int. Ed., 2015, 54, 2811-2815.