Biochemical and evolutionary characterization of the GNA gene family in Apicomplexa

Marta Cova

Glycosylphosphatidylinositol (GPI) anchors represent one of the major carbohydrate
modifications described in apicomplexan parasites such as Plasmodium and Cryptosporidium. Due to their important roles for the survival and pathogenicity of these organisms, GPI biosynthesis is a potential target to tackle relevant clinical and veterinarian infections caused by apicomplexan parasites. The generation of the UDP-N-acetylglucosamine (UDP-GlcNAc) precursor, needed to feed GPI biosynthesis, requires a glucosamine-phosphate N-acetyltransferase (GNA) activity not yet identified in apicomplexan parasites. Using different phylogenetic and comparative genomics
approaches, we identified two P. falciparum GNA candidates. One of them, designated as PfGNA, was able to rescue the growth of a Saccharomyces cerevisiae temperature
sensitive GNA mutant (ScGNA1-ts). PfGNA belongs to a gene family exclusively formed
by apicomplexan orthologs. Representatives from the main taxonomic families of the
phylum, including Cryptosporidium parvum, were also shown to complement ScGNA1-ts growth. Furthermore, we have confirmed PfGNA and C. parvum GNA enzymatic activities through in vitro activity assays. The independent evolution of Apicomplexa GNAs and the unique features of this protein family, together with the putative essentiality of GNA activity – which we are currently assessing – may reveal a novel drug target amenable for the rational design of selective inhibitors against apicomplexan parasites.