Identification and partial characterization of two eukaryotic UDP-galactopyranose mutases

Galactofuranose metabolism is valued as an important target for the development of new antituberculosis drugs. UDP-galactopyranose mutase, a central enzyme in galactofuranose biosynthesis, is essential for the growth and viability of mycobacteria. This enzyme catalyzes the conversion of UDP-galactopyranose into UDP-galactofuranose, the donor used by various galacto-furanosyltransferases. While D-galactofuranose residues are often found in important surface glycoconjugates of pathogenic bacteria, fungi and protozoan parasites, they are absent in the mammalian host, and thus their biosynthesis is an attractive target for the development of novel therapeutic strategies. In contrast to mycobacteria, the importance of galactofuranose for eukaryotic pathogens has not been ascertained because the enzymes involved in galactofuranose metabolism are unknown. Here, we report the identification and characterization of the first eukaryotic UDP-galactopyranose mutases. The genes encoding the enzymes were cloned from two different human pathogens: the parasite Leishmania major and the opportunistic fungus Aspergillus fumigatus. The newly identified eukaryotic enzymes exhibit 51% sequence identity, but are less than 20% identical to the prokaryotic counterparts. The sequence identity between pro- and eukaryotic enzymes is concentrated at amino acid residues that are involved in substrate and cofactor binding. Therefore, an inhibitor of UDP-galactopyranose mutase might be effective against a wide range of pathogenic organisms.