Eukaryotic UDP-Galactopyranose Mutase ( GLF Gene) in Microbial and Metazoal Pathogens

Abstract

ABSTRACT Galactofuranose (Gal f ) is a novel sugar absent in mammals but present in a variety of pathogenic microbes, often within glycoconjugates that play critical roles in cell surface formation and the infectious cycle. In prokaryotes, Gal f is synthesized as the nucleotide sugar UDP-Gal f by UDP-galactopyranose mutase (UGM) (gene GLF ). Here we used a combinatorial bioinformatics screen to identify a family of candidate eukaryotic GLF s that had previously escaped detection. GLF s from three pathogens, two protozoa ( Leishmania major and Trypanosoma cruzi ) and one fungus ( Cryptococcus neoformans ), had UGM activity when expressed in Escherichia coli and assayed in vivo and/or in vitro. Eukaryotic GLF s are closely related to each other but distantly related to prokaryotic GLF s, showing limited conservation of core residues around the substrate-binding site and flavin adenine dinucleotide binding domain. Several eukaryotes not previously investigated for Gal f synthesis also showed strong GLF homologs with conservation of key residues. These included other fungi, the alga Chlamydomonas and the algal phleovirus Feldmannia irregularis , parasitic nematodes ( Brugia , Onchocerca , and Strongyloides ) and Caenorhabditis elegans , and the urochordates Halocynthia and Cionia . The C. elegans open reading frame was shown to encode UGM activity. The GLF phylogenetic distribution suggests that Gal f synthesis may occur more broadly in eukaryotes than previously supposed. Overall, GLF /Gal f synthesis in eukaryotes appears to occur with a disjunct distribution and often in pathogenic species, similar to what is seen in prokaryotes. Thus, UGM inhibition may provide an attractive drug target in those eukaryotes where Gal f plays critical roles in cellular viability and virulence.