Purification and some properties of NAD-glycohydrolase from conidia of Neurospora crassa

The Fluorinated NAD Precursors Enhance FK866 Cytotoxicity by Activating SARM1 in Glioblastoma Cells

Glioblastoma, a formidable brain tumor characterized by dysregulated NAD metabolism, poses a significant therapeutic challenge. The NAMPT inhibitor FK866, which induces NAD depletion, has shown promise in controlling tumor proliferation and modifying the tumor microenvironment. However, the clinical efficacy of FK866 as a single drug therapy for glioma is limited. In this study, we aim to disrupt NAD metabolism using fluorinated NAD precursors and explore their synergistic effect with FK866 in inducing cytotoxicity in glioblastoma cells. The synthesized analogue of nicotinamide riboside (NR), ara-F nicotinamide riboside (F-NR), inhibits nicotinamide ribose kinase (NRK) activity in vitro, reduces cellular NAD levels, and enhances FK866's cytotoxicity in U251 glioblastoma cells, indicating a collaborative impact on cell death. Metabolic analyses reveal that F-NR undergoes conversion to fluorinated nicotinamide mononucleotide (F-NMN) and other metabolites, highlighting the intact NAD metabolic pathway in glioma cells. The activation of SARM1 by F-NMN, a potent NAD-consuming enzyme, is supported by the synergistic effect of CZ-48, a cell-permeable SARM1 activator. Temporal analysis underscores the sequential nature of events, establishing NAD depletion as a precursor to ATP depletion and eventual massive cell death. This study not only elucidates the molecular intricacies of glioblastoma cell death but also proposes a promising strategy to enhance FK866 efficacy through fluorinated NAD precursors, offering potential avenues for innovative therapeutic interventions in the challenging landscape of glioblastoma treatment.

Discovery of fungal surface NADases predominantly present in pathogenic species

Nicotinamide adenine dinucleotide (NAD) is a key molecule in cellular bioenergetics and signalling. Various bacterial pathogens release NADase enzymes into the host cell that deplete the host's NAD⁺ pool, thereby causing rapid cell death. Here, we report the identification of NADases on the surface of fungi such as the pathogen Aspergillus fumigatus and the saprophyte Neurospora crassa. The enzymes harbour a tuberculosis necrotizing toxin (TNT) domain and are predominately present in pathogenic species. The 1.6 Å X-ray structure of the homodimeric A. fumigatus protein reveals unique properties including N-linked glycosylation and a Ca²⁺-binding site whose occupancy regulates activity. The structure in complex with a substrate analogue suggests a catalytic mechanism that is distinct from those of known NADases, ADP-ribosyl cyclases and transferases. We propose that fungal NADases may convey advantages during interaction with the host or competing microorganisms.

Determination of ADP-ribosyl cyclase activity, cyclic ADP-ribose, and nicotinic acid adenine dinucleotide phosphate in tissue extracts

Cyclic ADP-ribose (cADPR) is a novel second messenger that releases calcium from intracellular stores. Although first shown to release calcium in the sea urchin egg, cADPR has been shown since to be active in a variety of cells and tissues, from plant to human. cADPR stimulates calcium release via ryanodine receptors although the mechanism is still not completely understood. cADPR is produced enzymatically from NAD by ADP-ribosyl cyclases; several of these proteins have been identified including one isolated from Aplysia californica, two types found in mammals (CD38 and CD157), and three forms in sea urchin. A cyclase activity has been measured in extracts from Arabidopsis thaliana although the protein is still unidentified. Nicotinic acid adenine dinucleotide phosphate (NAADP) is another novel messenger that releases calcium from internal stores and is produced by these same enzymes by an exchange reaction. NAADP targets lysosomal stores whereas cADPR releases calcium from the endoplasmic reticulum. Due to their importance in cell signaling, cADPR and NAADP have been the focus of numerous investigations over the last 25 years. This chapter describes several assay methods for the measurements of cADPR and NAADP concentration and cyclase activity in extracts from cells.

The design of new enzyme active sites for the catalysis of specific chemical reactions

Using appropriately designed coenzyme analogues, new active sites can be introduced into naturally occurring enzymes by the chemical modification of specific residues. Catalytic activities very different from those of the corresponding native enzymes can be observed in the resulting semisynthetic enzymes. Covalent modification of the SH group of the active site residue Cys-25 of papain with flavins like 8-bromoacetyl-10-methylisoalloxazine converts the enzyme into a highly effective oxidoreductase. Thus, the catalytic versatility of existing enzymes can be enhanced through 'chemical mutation' of the active site.

Purification of NAD glycohydrolase from Agkistrodon acutus venom

NAD glycohydrolase (NADase) from Agkistrodon acutus venom was purified to electrophoretic homogeneity by a fast, reproducible 3-step procedure including Q Sepharose Fast Flow, Superdex 75, and Mono S column chromatography. This new procedure gave a 15.6-fold purification with a recovery yield of 7.9% and a specific activity of 12.8 units/mg.

Vibrio fischeri genes hvnA and hvnB encode secreted NAD(+)-glycohydrolases

HvnA and HvnB are proteins secreted by Vibrio fischeri ES114, an extracellular light organ symbiont of the squid Euprymna scolopes, that catalyze the transfer of ADP-ribose from NAD(+) to polyarginine. Based on this activity, HvnA and HvnB were presumptively designated mono-ADP-ribosyltransferases (ARTases), and it was hypothesized that they mediate bacterium-host signaling. We have cloned hvnA and hvnB from strain ES114. hvnA appears to be expressed as part of a four-gene operon, whereas hvnB is monocistronic. The predicted HvnA and HvnB amino acid sequences are 46% identical to one another and share 44% and 34% identity, respectively, with an open reading frame present in the Pseudomonas aeruginosa genome. Four lines of evidence indicate that HvnA and HvnB mediate polyarginine ADP-ribosylation not by ARTase activity, but indirectly through an NAD(+)-glycohydrolase (NADase) activity that releases free, reactive, ADP-ribose: (i) like other NADases, and in contrast to the ARTase cholera toxin, HvnA and HvnB catalyzed ribosylation of not only polyarginine but also polylysine and polyhistidine, and ribosylation was inhibited by hydroxylamine; (ii) HvnA and HvnB cleaved 1, N(6)-etheno-NAD(+) and NAD(+); (iii) incubation of HvnA and HvnB with [(32)P]NAD(+) resulted in the production of ADP-ribose; and (iv) purified HvnA displayed an NADase V(max) of 400 mol min(-1) mol(-1), which is within the range reported for other NADases and 10(2)- to 10(4)-fold higher than the minor NADase activity reported in bacterial ARTase toxins. Construction and analysis of an hvnA hvnB mutant revealed no other NADase activity in culture supernatants of V. fischeri, and this mutant initiated the light organ symbiosis and triggered regression of the light organ ciliated epithelium in a manner similar to that for the wild type.

Auto-ADP-ribosylation of NAD glycohydrolase from Neurospora crassa

NAD glycohydrolase (NADase; EC 3.2.2.5) is an enzyme that catalyzes hydrolysis of NAD to produce ADP-ribose and nicotinamide. We recently demonstrated that self-inactivation of NADase from rabbit erythrocytes was due to an auto-ADP-ribosylation. In the present study, a mechanism of self-inactivation of NADase from Neurospora crassa by its substrate was investigated by using intact mycelia of N. crassa and purified NADase, which had molecular characteristics different from mammalian NADases. The results suggested that inactivation of NADase from N. crassa was also due to an auto-ADP-ribosylation. These findings indicate that the auto-modification of NADase is one of the universal phenomena to regulate enzyme functions.

Hydrophobic properties of NAD glycohydrolase from neurospora crassa conidia and interaction with dioxane

NAD glycohydrolase (NADase, EC 3.2.2.5) from Neurospora crassa conidia shows marked hydrophobic properties which are related to the self inhibition of the enzyme. Both aliphatic amines and carboxylic acids are able to inhibit noncompetitively the catalytic activity of the enzyme and the inhibition depends on the non-polar moiety of the substances. Also dioxane is an inhibitor of NAD glycohydrolase even though it apparently increases the specific activity of the enzyme. This effect can be explained by the fact that NADase is present as a dimer when the enzyme is concentrated or at high temperature, and dioxane binds the enzyme breaking the hydrophobic bonds in the dimeric enzyme and yielding the most active monomeric form which is only slightly inhibited by the organic solvent.

Purification of NAD glycohydrolase from Neurospora crassa conidia by a polyclonal immunoadsorbent

NAD glycohydrolase from Neurospora crassa conidia was purified by affinity chromatography on a column of polyclonal antibodies bound to an agarose matrix. The procedure was easy, non-denaturating and suitable for repetitive use of the gel. The enzyme obtained appeared homogeneous by sodiumdodecyl sulphate-polyacrylamide gel electrophoresis.

High-performance liquid chromatography determination of enzyme activities in the presence of small amounts of product

Enzymes can be assayed by HPLC by calculating the amount of substrate(s) left over, or product formed, through the peak area ratios with a suitable internal standard. However, sometimes the substrates used are contaminated with small amounts of products and this can lead to errors in the determination of the enzyme activity. A method for a HPLC test of such enzymes, which prevents eventual errors, uses the ratio substrate/product at time zero as internal standard and the kinetics can be followed with the aid of a simple mathematical equation. This approach was applied to the determination of the activities of papain, urokinase, NAD glycohydrolase, and pyruvate kinase samples and it was compared with the data obtained by the internal standard method, giving reproducible results in all cases.

Preparation of immobilized NAD glycohydrolase from Neurospora crassa conidia by hydrophobic interaction--characteristics of the enzyme derivative

NAD glycohydrolase from Neurospora crassa conidia has been immobilized by hydrophobic interaction on Sepharose 4B beads coated with propyl residues through CNBr activation. The bond resulted stable under a wide range of conditions (ionic strength, temperature, pH). As a result of immobilization the pH optimum for catalytic activity shifted by about 0.2 pH unit in the acidic direction, to lie between 7.5 and 7.3. The stability of the enzymatic activity was largely enhanced by effect of immobilization but the Km value towards NAD+ was increased compared with that of the free enzyme (1 X 10(-3) and 2 X 10(-4) M respectively).

High-performance liquid chromatography for assaying NAD glycohydrolase from Neurospora crassa conidia

A rapid and sensitive high-performance liquid chromatographic technique was developed to determinate NAD glycohydrolase (EC 3.2.2.5.) activity from Neurospora crassa conidia. The separation of the assay substrate and products was achieved by isocratic reverse-phase chromatography and the peaks were detected by the absorbance at 259 nm. Quantities of NAD+ and nicotinamide as small as 10 pmol could be measured.