Open and Closed Structures of the UDP-glucose Pyrophosphorylase from Leishmania major

Abstract

Uridine diphosphate-glucose pyrophosphorylase (UGPase) represents a ubiquitous enzyme, which catalyzes the formation of UDP-glucose, a key metabolite of the carbohydrate pathways of all organisms. In the protozoan parasite Leishmania major, which causes a broad spectrum of diseases and is transmitted to humans by sand fly vectors, UGPase represents a virulence factor because of its requirement for the synthesis of cell surface glycoconjugates. Here we present the crystal structures of the L. major UGPase in its uncomplexed apo form (open conformation) and in complex with UDP-glucose (closed conformation). The UGPase consists of three distinct domains. The N-terminal domain exhibits species-specific differences in length, which might permit distinct regulation mechanisms. The central catalytic domain resembles a Rossmann-fold and contains key residues that are conserved in many nucleotidyltransferases. The C-terminal domain forms a left-handed parallel ␤-helix (L␤H), which represents a rarely observed structural element. The presented structures together with mutagenesis analyses provide a basis for a detailed analysis of the catalytic mechanism and for the design of species-specific UGPase inhibitors.Uridinediphosphate-glucose pyrophosphorylase (UGPase; EC 2.7.7.9) 2 is present in all three kingdoms of life and catalyzes the reaction of UTP ϩ glucose 1-phosphate 3 UDP-glucose ϩ PP i in the presence of Mg 2ϩ in vivo. UDP-glucose, the activated form of glucose, plays an essential role in the metabolism of carbohydrates in all organisms. UDP-glucose is the main glucosyl donor for the formation of glycogen, starch, and cellulose, as well as for the synthesis of glucose-containing glycolipids, glycoproteins, and proteoglycans (1, 2). In addition, other important nucleotide sugars such as UDP-xylose, UDP-glucuronic acid, and UDP-galactose are derived from UDP-glucose. In bacteria some of these activated sugars are used to build the bacterial polysaccharide capsule that often represents the sole determinant of virulence of these organisms. In Streptococcus pneumoniae, for example, it was known that mutants containing an inactivated UGPase gene (galU) are completely avirulent, as they are unable to form the polysaccharide capsule (3). Similarly, UGPase is involved in the biosynthesis of the lipopolysaccharide core in Escherichia coli, resulting in a reduced adhesion behavior of E. coli galU mutants (4).The protozoan parasite Leishmania is the causative agent of a widespread group of diseases collectively known as Leishmaniasis. The disease affects more than 12 million people worldwide and until now there is no specific drug available to cure the disease.3 Leishmania express various glycoconjugates on their cell surface that is dynamically modified during the parasite life cycle allowing the survival and proliferation in the sand fly vector as well as in the mammalian host (6, 7).The biosynthesis of glycoconjugates essentially depends on the availability of activated nucleotide sugars. UGPase represents a key position in...

Leishmania UDP-sugar Pyrophosphorylase

“…This phenomenon, suggestive of an ordered bi-substrate mechanism with UTP binding preceding the hexose 1-phosphate entry, was previously observed with the LmjUGP, and a conformational change was proposed (22). The subsequently determined x-ray crystal structure clearly revealed a conformational change upon complexion with UTP (26). It is therefore not unreasonable to assume that USP binds UTP in a similar mode.…”

“…major USP presents a clear homology with plant USPs and a modest but significant homology with UGPs and UDP-N-acetylglucosamine pyrophosphorylases over the entire sequence. In particular, the pyrophosphorylase glycine-rich consensus motif (25,26) essential for catalysis is highly conserved and additional residues involved in uridine and phosphate binding. As highlighted by STD NMR spectroscopic studies, interactions of the uridine moiety of nucleotide sugars or UTP with LmjUSP are similar to those observed with LmjUGP and play a significant role in substrate binding.…”

“…2A and highlights the conservation of residues essential for catalytic activity of pyrophosphorylase and for nucleotide sugar binding (25,26). The LmjUSP basic residues Lys-134, His-224, and Lys-434 (corresponding to LmjUGP Lys-95, His-191, and Lys-380) are strictly conserved and predicted to be involved in phosphate binding (26). Similarly, with the exception of Val-120, which is a lysine residue in UGPs, the amino acids involved in uridine binding are preserved.…”

Redox regulation of UDP-glucose pyrophosphorylase from Entamoeba histolytica

“…The reaction catalyzed by pyrophosphorylases is freely reversible in vitro, with an equilibrium close to 1; although differences were found respect to rates of the forward or reverse reaction [26], which could be attributed to regulation or characteristics associated with protein oligomerization [6,27]. Data in Table 2 indicate that the EhiUDP-GlcPPase exhibited lower V max and affinity for substrates than the enzyme from L. major [5,7], Arabidopsis thaliana [28], and barley [29]; whereas kinetics for the recombinant enzyme are similar than those reported for one specific UDP-GlcPPase partially purified from E. histolytica [30], except for a lower affinity of the former for UTP. In our hands, the entamoebic enzyme was not able to utilize ATP, GTP, TTP, or mannose-1-P as substrates, these results agreeing with the previous characterization of the enzyme purified from cells of the protozoan [30].…”

“…Less is known about specific biosynthetic pathways in E. histolytica rendering PPG or any other complex glycoconjugate. Production of structural oligoand polysaccharides occurs via UDP-Glc in different organisms [4,5]. The sugarenucleotide is synthesized from glucose-1-phosphate (Glc1P) and UTP in a reaction catalyzed by UDP-Glc pyrophosphorylase (EC 2.7.7.9; UDP-GlcPPase) [6e8].…”