Cloning and characterisation of the UDP-glucose 4′-epimerase of Trypanosoma cruzi

Trypanosoma cruzi incorporates galactose into many of its cell-surface glycoconjugates but it is unable to transport this sugar through its hexose transporter. Epimerisation of UDP-glucose to UDP-galactose by UDP-glucose 4′-epimerase may be the only way that the parasites can obtain galactose. Here, we describe cloning the T. cruzi UDP-Glc 4′-epimerase (TcGALE) gene and show that it is functional by complementing an Escherichia coli epimerase-deficient strain. The T. cruzi GALE gene encodes a 42.4kDa protein and the recombinant protein expressed in E. coli is a homodimer in solution with a specific activity of 3.8Umg−1 and Km for UDP-Gal of 114μM. Unlike the human epimerase, T. cruzi UDP-Glc 4′-epimerase is unable to inter-convert UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine. This may explain why T. cruzi initiates O-glycosylation of its abundant GPI-anchored surface mucins via GlcNAcα1-O-Thr/Ser rather than the GalNAcα1-O-Thr/Ser linkage that is common for mucins from many other eukaryotes.