Probing UDP-galactopyranose mutase binding pocket: A dramatic effect on substitution of the 6-position of UDP-galactofuranose

UDP-galactopyranose mutase (UGM) catalyzes the isomerization of UDP-galactopyranose (UDP-Gal p) into UDP-galactofuranose (UDP-Gal f), an essential step of the mycobacterial cell wall biosynthesis. UDP-(6-deoxy-6-fluoro)- d-galactofuranose 1 was tested as substrate of UGM. Turnover could be observed by HPLC. The k cat (7.4 s −1) and the K m (24 mM) of 1 were thus measured and compared with those of UDP-Gal f and other fluorinated analogs. The presence of the fluorine atom at the 6-position had a moderate effect on the rate of the reaction but a huge one on the interactions between the enzyme and its substrate. This result demonstrated that key interactions occur at the vicinity of the 6-position of UDP-galactose in the Michaelis complex.