Mononucleotide Adenylyltransferase Research Articles

In vitro and in silico study of an exclusive insertion in the nicotinamide/nicotinate mononucleotide adenylyltransferase from Leishmania braziliensis

The intracellular parasite Leishmania braziliensis is the causal agent of cutaneous and mucocutaneous leishmaniasis, a group of endemic diseases in tropical regions, including Latin America. New therapeutic targets are required to inhibit the pathogen without affecting the host. The enzyme nicotinamide/nicotinate mononucleotide adenylyltransferase (NMNAT; EC: 2.7.7.1/18) is a potential target, since it catalyzes the final step in the biosynthesis of nicotinamide adenine dinucleotide (NAD+), which is an essential metabolite in multiple cellular processes. In this work, we produced and evaluated the catalytic activity of the recombinant protein 6HisΔ241-249LbNMNAT to study the functional relevance of the exclusive insertion present in the enzyme of L. braziliensis (LbNMNAT), but absent in the primary structure of human NMNATs. Our results indicate that the 241–249 insertion constitutes a structural element that connects the protein structure Rossmann topology with the carboxyl-terminal domain of the enzyme. The removal of this region drastically decreases the solubility, and enzymatic activity of the recombinant, causing its inactivation. Molecular dynamics simulations were carried out with the wild-type and truncated enzymes to verify additional changes in their stability, which indicated a better stability in the wild-type protein. These findings constitute an initial step to identify a new inhibition mechanism for the development of focused pharmacological strategies on exclusive insertions from the LbNMNAT protein.

Identification and sub-cellular localization of a NAD transporter in Leishmania braziliensis (LbNDT1)

Nicotinamide adenine dinucleotide (NAD) is one of the central molecules involved in energy homeostasis, cellular signaling and antioxidative defense systems. Consequently, its biosynthetic pathways and transport systems are of vital importance. The nicotinamide/nicotinate mononucleotide adenylyltransferase (NMNAT), a key enzyme in the biosynthesis of NAD, is distributed in all domains of life and exhibits various isoforms in free-living organisms in contrast with intracellular parasites, which displays a single enzyme. In Leishmania braziliensis a unique cytosolic NMNAT has been reported to date and the mechanisms through which adequate levels of NAD are maintained among the different sub-cellular compartments of this parasite are unknown. Experimental evidences have related the transport of NAD to the Nucleotide Transporters (NTTs) family, whose members are located in the cytoplasmic membrane of parasitic life organisms. Additionally, the Mitochondrial Carrier Family (MCF), a group of proteins located in the membrane of internal organelles such as the mitochondria of free life organisms, has been implicated in NAD transport. Applying bioinformatics tools, the main characteristics of the MCF were found in a transporter candidate that we have designated as Nicotinamide Adenine Dinucleotide Transporter 1 of L. braziliensis (LbNDT1). The expression of LbNDT1 was tested both in axenic amastigotes and promastigotes of L. braziliensis, through immunodetection using polyclonal avian antibodies produced in this study. N-glycosylation of LbNDT1 was observed in both stages. Additionally, a possible partial mitochondrial distribution for LbNDT1 in amastigotes and a possible glycosomal location in promastigotes are proposed. Finally, the capability of LbNDT1 to transport NAD was confirmed by complementation assays in Saccharomyces cerevisiae. Our results demonstrate the existence of LbNDT1 in L. braziliensis becoming the first NAD transporter identified in protozoan parasites to date.

Kinetic and oligomeric study of Leishmania braziliensis nicotinate/nicotinamide mononucleotide adenylyltransferase

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme involved in REDOX reactions and oxidative stress defense systems. Furthermore, NAD is used as substrate by proteins that regulate essential cellular functions as DNA repair, genetic, and signal transduction, among many others. NAD biosynthesis can be completed through the de novo and salvage pathways, which converge at the common step catalyzed by the nicotinate/nicotinamide mononucleotide adenylyltransferase (NMNAT EC: 2.7.7.1/18). Here, we report the kinetic characterization of the NMNAT of Leishmania braziliensis (LbNMNAT), one of the etiological agents of leishmaniasis, a relevant parasitic disease. The expression and homogeneous purification of the recombinant 6xHis-LbNMNAT protein was carried out and its kinetic study, which included analysis of Km, Vmax, Kcat and the equilibrium constant (KD) for both the forward and reverse reactions, was completed. The oligomeric state of the recombinant 6xHis-LbNMNAT protein was studied through size exclusion chromatography. Our results indicated the highest and lowest Km values for ATP and NAD, respectively. According to the calculated KD, the pyrophosphorolytic cleavage of NAD is favored in vitro. Moreover, the recombinant 6xHis-LbNMNAT protein showed a monomeric state, although it exhibits a structural element involved in potential subunits interaction. Altogether, our results denote notable differences of the LbNMNAT protein in relation to the human orthologs HsNMNAT1-3. These differences constitute initial findings that have to be continued to finally propose the NMNAT as a promissory pharmacological target in L. braziliensis.

Localization and phosphorylation of Plasmodium falciparum nicotinamide/nicotinate mononucleotide adenylyltransferase (PfNMNAT) in intraerythrocytic stages

BackgroundNicotinamide adenine dinucleotide (NAD+) is an essential molecule in the energy metabolism of living beings, and it has various cellular functions. The main enzyme in the biosynthesis of this nucleotide is nicotinamide/nicotinate mononucleotide adenylyltransferase (NMNAT, EC 2.7.7.1/18) because it is the convergence point for all known biosynthetic pathways. NMNATs have divergences in both the number of isoforms detected and their distribution, depending on the organism.MethodsIn the laboratory of basic research in biochemistry (LIBBIQ: acronym in Spanish) the NMNATs of protozoan parasites (Leishmania braziliensis, Plasmodium falciparum, Trypanosoma cruzi, and Giardia duodenalis) have been studied, analysing their catalytic properties through the use of proteins. Recombinants and their cellular distribution essentially. In 2014, O’Hara et al. determined the cytoplasmic localization of NMNAT of P. falciparum, using a transgene coupled to GFP, however, the addition of labels to the study protein can modify several of its characteristics, including its sub-cellular localization.ResultsThis study confirms the cytoplasmic localization of this protein in the parasite through recognition of the endogenous protein in the different stages of the asexual life cycle. Additionally, the study found that PfNMNAT could be a phosphorylation target at serine, tyrosine and threonine residues, and it shows variations during the asexual life cycle.ConclusionsThese experiments confirmed that the parasite is situated in the cytoplasm, fulfilling the required functions of NAD+ in this compartment, the PfNMNAT is regulated in post-transcription processes, and can be regulated by phosphorylation in its residues.

Nicotinamide mononucleotide adenylyltransferase of Trypanosoma cruzi (TcNMNAT): a cytosol protein target for serine kinases.

Nicotinamide/nicotinate adenine dinucleotide (NAD+/NaAD) performs essential functions in cell metabolism and energy production due to its redox properties. The nicotinamide/nicotinate mononucleotide adenylyltransferase (NMNAT, EC 2.7.7.1/18) enzyme catalyses the key step in the biosynthesis of NAD+. Previously, the enzyme NMNAT was identified in Trypanosoma cruzi (TcNMNAT), a pathogenic agent with epidemiological importance in Latin America. To continue with the functional characterisation of this enzyme, its subcellular location and its possible post-translational modifications were examined in this study. For this, polyclonal antibodies were generated in mice, with soluble and denatured recombinant protein being used to detect the parasite’s NMNAT. Immunodetection assays were performed on whole extracts of T. cruzi, and an approximation of its intracellular location was determined using confocal microscopy on wild and transgenic parasites, which revealed the cytosol distribution patterns. This localisation occurs according to the needs of the dinucleotides that exist in this compartment. Additionally, a bioinformatics study was performed as a first approach to establish the post-translational modifications of the enzyme. Possible phosphorylation events were experimentally analysed by western blot, highlighting TcNMNAT as a potential target for serine kinases.

Identification of a nicotinamide/nicotinate mononucleotide adenylyltransferase in Giardia lamblia (GlNMNAT)

Giardia lamblia is an intestinal protozoan parasite that causes giardiasis, a disease of high prevalence in Latin America, Asia and Africa. Giardiasis leads to poor absorption of nutrients, severe electrolyte loss and growth retardation. In addition to its clinical importance, this parasite is of special biological interest due to its basal evolutionary position and simplified metabolism, which has not been studied thoroughly. One of the most important and conserved metabolic pathways is the biosynthesis of nicotinamide adenine dinucleotide (NAD). This molecule is widely known as a coenzyme in multiple redox reactions and as a substrate in cellular processes such as synthesis of Ca2+ mobilizing agents, DNA repair and gene expression regulation. There are two pathways for NAD biosynthesis, which converge at the step catalyzed by nicotinamide/nicotinate mononucleotide adenylyltransferase (NMNAT, EC 2.7.7.1/18). Using bioinformatics tools, we found two NMNAT sequences in Giardia lamblia (glnmnat-a and glnmnat-b). We first verified the identity of the sequences in silico. Subsequently, glnmnat-a was cloned into an expression vector. The recombinant protein (His-GlNMNAT) was purified by nickel-affinity binding and was used in direct in vitro enzyme assays assessed by C18-HPLC, verifying adenylyltransferase activity with both nicotinamide (NMN) and nicotinic acid (NAMN) mononucleotides. Optimal reaction pH and temperature were 7.3 and 26 °C. Michaelis–Menten kinetics were observed for NMN and ATP, but saturation was not accomplished with NAMN, implying low affinity yet detectable activity with this substrate. Double-reciprocal plots showed no cooperativity for this enzyme. This represents an advance in the study of NAD metabolism in Giardia spp.

Synthesizing and Salvaging NAD+: Lessons Learned from Chlamydomonas reinhardtii

The essential coenzyme nicotinamide adenine dinucleotide (NAD+) plays important roles in metabolic reactions and cell regulation in all organisms. Bacteria, fungi, plants, and animals use different pathways to synthesize NAD+. Our molecular and genetic data demonstrate that in the unicellular green alga Chlamydomonas NAD+ is synthesized from aspartate (de novo synthesis), as in plants, or nicotinamide, as in mammals (salvage synthesis). The de novo pathway requires five different enzymes: L-aspartate oxidase (ASO), quinolinate synthetase (QS), quinolate phosphoribosyltransferase (QPT), nicotinate/nicotinamide mononucleotide adenylyltransferase (NMNAT), and NAD+ synthetase (NS). Sequence similarity searches, gene isolation and sequencing of mutant loci indicate that mutations in each enzyme result in a nicotinamide-requiring mutant phenotype in the previously isolated nic mutants. We rescued the mutant phenotype by the introduction of BAC DNA (nic2-1 and nic13-1) or plasmids with cloned genes (nic1-1 and nic15-1) into the mutants. NMNAT, which is also in the de novo pathway, and nicotinamide phosphoribosyltransferase (NAMPT) constitute the nicotinamide-dependent salvage pathway. A mutation in NAMPT (npt1-1) has no obvious growth defect and is not nicotinamide-dependent. However, double mutant strains with the npt1-1 mutation and any of the nic mutations are inviable. When the de novo pathway is inactive, the salvage pathway is essential to Chlamydomonas for the synthesis of NAD+. A homolog of the human SIRT6-like gene, SRT2, is upregulated in the NS mutant, which shows a longer vegetative life span than wild-type cells. Our results suggest that Chlamydomonas is an excellent model system to study NAD+ metabolism and cell longevity.

WldS requires Nmnat1 enzymatic activity and N16–VCP interactions to suppress Wallerian degeneration

Slow Wallerian degeneration (WldS) encodes a chimeric Ube4b/nicotinamide mononucleotide adenylyl transferase 1 (Nmnat1) fusion protein that potently suppresses Wallerian degeneration, but the mechanistic action of WldS remains controversial. In this study, we characterize WldS-mediated axon protection in vivo using Drosophila melanogaster. We show that Nmnat1 can protect severed axons from autodestruction but at levels significantly lower than WldS, and enzyme-dead versions of Nmnat1 and WldS exhibit severely reduced axon-protective function. Interestingly, a 16–amino acid N-terminal domain of WldS (termed N16) accounts for the differences in axon-sparing activity between WldS and Nmnat1, and N16-dependent enhancement of Nmnat1-protective activity in WldS requires the N16-binding protein valosin-containing protein (VCP)/TER94. Thus, WldS-mediated suppression of Wallerian degeneration results from VCP–N16 interactions and Nmnat1 activity converging in vivo. Surprisingly, mouse Nmnat3, a mitochondrial Nmnat enzyme that localizes to the cytoplasm in Drosophila cells, protects severed axons at levels indistinguishable from WldS. Thus, nuclear Nmnat activity does not appear to be essential for WldS-like axon protection.