Sucrose phosphorylase fromAlteromonas mediterranea: structural insight into the regioselective α-glucosylation of (+)-catechin

Abstract Flavonoids glycosylation at different positions is paramount to solubility and modulation of bioactivities. Sucrose phosphorylases, through transglycosylation reactions, are interesting enzymes that can transfer glucose from sucrose, the donor substrate, onto polyphenols to form glycoconjugates. Here, we report for the first time the structural and enzymatic properties of sucrose phosphorylase from the marine bacteria Alteromonas mediterranea ( Am SP). We characterized and investigated the transglucosylation capacity of two new variants of the enzyme on (+)-catechin and their propensity to catalyse its regioselective glucosylation. Am SP-Q353F and Am SP-P140D were shown to catalyse the regiospecific glucosylation of (+)-catechin using sucrose as donor substrate. While AmSP-WT was devoid of synthetic activity, each of its two single mutant provided high yields of specific regioisomers: 89% of (+)-catechin-4′-O-α-D-glucopyranoside (CAT-4’) for AmSP-P140D and 92% of (+)-catechin-3′-O-α-D-glucopyranoside (CAT-3’) for AmSP-Q353F. The novel compound CAT-4’ was fully characterized by NMR and mass spectrometry. We used molecular docking simulations on structural models of the glucosyl-enzyme intermediate to explain this regioselectivity. We showed that Am SP-P140D preferentially binds (+)-catechin in a mode that favours glucosylation on its hydroxyl group in position 4’ (OH-4’) while the binding mode of the flavonoid in AmSP-Q353F favoured glucosylation on its hydroxyl group in position 3’ (OH-3’).