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-Galp) into UDP-galactofuranose (UDP-Galf), 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- Galf 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 UDPgalactose in the Michaelis complex. (C) 2009 Elsevier Ltd. All rights reserved.