CONICET | Buscador de Institutos y Recursos Humanos

Background: Giardia lamblia is a pathogen of humans and other vertebrates. The synthesis of glycogen and of structural oligo and polysaccharides critically determine the parasite´s capacity for survival and pathogenicity. These characteristics establish that UDP-glucose is a relevant metabolite, as it is a main substrate to initiate varied carbohydrate metabolic routes.Results: Herein, we report the molecular cloning of the gene encoding UDP-glucose pyrophosphorylase from genomic DNA of G. lamblia, followed by its heterologous expression in Escherichia coli. Thepurified recombinant enzyme was characterized to have a monomeric structure. Glucose-1-phosphate and UTP were preferred substrates, but the enzyme also used galactose-1-phosphate and TTP. The catalytic efficiency to synthesizeUDP-galactose was significant. Oxidation by physiological compounds (hydrogen peroxide and nitric oxide) inactivated the enzyme and the process was reverted after reduction by cysteine and thioredoxin. UDP-Nacetyl-glucosamine pyrophosphorylase, the other UTP-related enzyme in the parasite, neither used galactose-1-phosphate nor was affected by redox modification.Conclusions: Our results suggest that in G. lamblia the UDP-glucose pyrophosphorylase is regulated by oxidoreduction mechanism. The enzyme exhibits the ability to synthesize UDP-glucose and UDP-galactose and it plays a key role providing substrates to glycosyl transferases that produce oligo and polysaccharides.General significance: The characterization of the G. lamblia UDP-glucose pyrophosphorylase reinforces the view that in protozoa this enzyme is regulated by a redox mechanism. As well, we propose a new pathway for UDPgalactose production mediated by the promiscuous UDP-glucose pyrophosphorylase of this organism.

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