Structure and function of nicotinamide mononucleotide adenylyltransferase

The enzyme nicotinamide mononucleotide adenylyltransferase (NMNAT), a member of the nucleotidyltransferase alpha/beta phosphodiesterase superfamily, catalyzes the reaction NMN + ATP = NAD + PPi, representing the final step in the biosynthesis of NAD, a molecule playing a fundamental role as a cofactor in cellular redox reactions. NAD also serves as the substrate for reactions involved in important regulatory roles, such as protein covalent modifications, like ADP-ribosylation reactions, as well as Sir2 histone deacetylase, a recently discovered class of enzymes involved in the regulation of gene silencing. This overview describes the most recent findings on NMNATs from bacteria, archaea, yeast, animal and human sources, with detailed consideration of their major kinetic, molecular and structural features. On this regard, the different characteristics exhibited by the enzyme from the various species are highlighted. The possibility that NMNAT may represent an interesting candidate as a target for the rational design of selective chemotherapeutic agents has been suggested.

Enzymology of NAD+ homeostasis in man

This review describes the enzymes involved in human pyridine nucleotide metabolism starting with a detailed consideration of their major kinetic, molecular and structural properties. The presentation encompasses all the reactions starting from the de novo pyridine ring formation and leading to nicotinamide adenine dinucleotide (NAD(+)) synthesis and utilization. The regulation of NAD(+) homeostasis with respect to the physiological role played by the enzymes both utilizing NAD(+) through the nonredox NAD(+)-dependent reactions and catalyzing the recycling of the common product, nicotinamide, is discussed. The salient features of other enzymes such as NAD(+) pyrophosphatase, nicotinamide mononucleotide 5'-nucleotidase, nicotinamide riboside kinase and nicotinamide riboside phosphorylase, described under 'miscellaneous', are likewise presented.

Inflammatory bowel disease and hospital treatment in Italy: the RING multi-centre study

AIM

To explore the management of chronic inflammatory bowel disease, specifically Crohn's disease and ulcerative colitis, in Italian gastroenterology units.

METHODS

The RING (Ricerca Informatizzata in Gastroenterologia) project is an observational study collecting hospital discharge forms from 56 centres. Factors associated with the length of hospital stay were studied using multivariate logistic regression.

RESULTS

In 24 months starting from August 2000, out of 29,376 hospital discharge forms, 2131 (7.3%) were collected for inflammatory bowel disease (1163 for Crohn's disease and 968 for ulcerative colitis). The Crohn's disease and ulcerative colitis groups were compared according to demographic characteristics, diagnoses, procedures and hospital stay. In Crohn's disease, computed tomography/magnetic resonance imaging, x-rays/barium enema, number of procedures and number of diagnoses were significantly associated with a hospital stay longer than 10 days. In ulcerative colitis, this association was found for parenteral nutrition, malnutrition, computed tomography/magnetic resonance imaging and number of procedures.

CONCLUSIONS

Crohn's disease was confirmed as a disabling disorder requiring more frequent hospital treatment than ulcerative colitis. For the latter, parenteral nutrition and malnutrition were related to a longer hospital stay. The number of procedures, especially abdominal computed tomography/magnetic resonance imaging, was a major item for both pathologies.

Dinucleoside polyphosphate NAD analogs as potential NMN adenylyltransferase inhibitors. Synthesis and biological evaluation

Two dinucleoside polyphosphate NAD analogs, P1-(adenosine-5')-P3-(nicotinamide riboside-5')triphosphate (Np3A, 1) and P1-(adenosine-5')-P4-(nicotinamide riboside-5')tetraphosphate (Np4A, 2), were synthesized and tested as inhibitors of both microbial and human recombinant NMN adenylyltransferase. Compounds 1 and 2 proved to be selective inhibitors of microbial enzymes.

Thyroid abscess associated with a substernal goiter. Case report

An abscess associated with an intrathoracic goiter is an extremely rare condition. The authors report a case of a thyroid abscess complicated by acute dyspnea and asphyxia in a patient of geriatric age with a substernal goiter. Surgical therapy was necessary to obtain a correct diagnosis and an effective treatment.

Serum cholesterol and psychological distress in hospitalized depressed patients

OBJECTIVE

To assess the relationship between total serum cholesterol and various psychosocial variables in depressed in-patients.

METHOD

One hundred and eighty-six patients had their total fasting serum cholesterol assessed following admission; psychiatric diagnoses were obtained with the structured clinical interview for DSM-IV (SCID) interview. Psychopathology was measured with a clinician rated scale [Montgomery and Asberg Depressive Rating Scale (MADRS)] and a self-rating scale [Symptom checklist-90 (SCL-90)].

RESULTS

Univariate analyses showed lower total serum cholesterol levels being correlated with higher scores in several psychopathological areas. Multivariate analyses indicated that male gender, lower age and higher MADRS scores were the most predictive variables for lower cholesterol levels.

CONCLUSION

The data suggest, in this depressed population, an association between serum cholesterol and depressive symptoms. What is the cause and what is its effect is not possible to say from this cross-sectional study.

Wallerian degeneration of injured axons and synapses is delayed by a Ube4b/Nmnat chimeric gene

Axons and their synapses distal to an injury undergo rapid Wallerian degeneration, but axons in the C57BL/WldS mouse are protected. The degenerative and protective mechanisms are unknown. We identified the protective gene, which encodes an N-terminal fragment of ubiquitination factor E4B (Ube4b) fused to nicotinamide mononucleotide adenylyltransferase (Nmnat), and showed that it confers a dose-dependent block of Wallerian degeneration. Transected distal axons survived for two weeks, and neuromuscular junctions were also protected. Surprisingly, the Wld protein was located predominantly in the nucleus, indicating an indirect protective mechanism. Nmnat enzyme activity, but not NAD+ content, was increased fourfold in WldS tissues. Thus, axon protection is likely to be mediated by altered ubiquitination or pyridine nucleotide metabolism.

Genetic basis of hemolytic anemia caused by pyrimidine 5' nucleotidase deficiency

Pyrimidine 5' nucleotidase (P5'N-1) deficiency is an autosomal recessive condition causing hemolytic anemia characterized by marked basophilic stippling and the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. It is implicated in the anemia of lead poisoning and is possibly associated with learning difficulties. Recently, a protein with P5'N-1 activity was analyzed and a provisional complementary DNA (cDNA) sequence published. This sequence was used to study 3 families with P5'N-1 deficiency. This approach generated a genomic DNA sequence that was used to search GenBank and identify the gene for P5'N-1. It is found on chromosome 7, consists of 10 exons with alternative splicing of exon 2, and produces proteins 286 and 297 amino acids long. Three homozygous mutations were identified in this gene in 4 subjects with P5'N-1 deficiency: codon 98 GAT-->GTT, Asp-->Val (linked to a silent polymorphism codon 92, TAC-->TAT), codon 177, CAA-->TAA, Gln-->termination, and IVS9-1, G-->T. The latter mutation results in the loss of exon 9 (201 bp) from the cDNA. None of these mutations was found in 100 normal controls. The DNA analysis was complicated by P5'N-1 pseudogenes found on chromosomes 4 and 7. This study is the first description of the structure and location of the P5'N-1 gene, and 3 mutations have been identified in affected patients from separate kindreds. (Blood. 2001;97:3327-3332)

Molecular cloning, chromosomal localization, tissue mRNA levels, bacterial expression, and enzymatic properties of human NMN adenylyltransferase

A 1329-base pair clone isolated from a human placenta cDNA library contains a full-length 837-base pair coding region for a 31.9-kDa protein whose deduced primary structure exhibits high homology to consensus sequences found in other NMN adenylyltransferases. Northern blotting detected a major 3.1-kilobase mRNA transcript as well as a minor 4.1-kilobase transcript in all human tissues examined. In several cancer cell lines, lower levels of mRNA expression were clearly evident. The gene encoding the human enzyme was mapped to chromosome band 1p32-35. High efficiency bacterial expression yielded 1.5 mg of recombinant enzyme/liter of culture medium. The molecular and kinetic properties of recombinant human NMN adenylyltransferase provide new directions for investigating metabolic pathways involving this enzyme.

Structure of nicotinamide mononucleotide adenylyltransferase: a key enzyme in NAD(+) biosynthesis

BACKGROUND

Nicotinamide adenine dinucleotide (NAD(+)) is an essential cofactor involved in fundamental processes in cell metabolism. The enzyme nicotinamide mononucleotide adenylyltransferase (NMN AT) plays a key role in NAD(+) biosynthesis, catalysing the condensation of nicotinamide mononucleotide and ATP, and yielding NAD(+) and pyrophosphate. Given its vital role in cell life, the enzyme represents a possible target for the development of new antibacterial agents.

RESULTS

The structure of NMN AT from Methanococcus jannaschii in complex with ATP has been solved by X-ray crystallography at 2.0 A resolution, using a combination of single isomorphous replacement and density modification techniques. The structure reveals a hexamer with 32 point group symmetry composed of alpha/beta topology subunits. The catalytic site is located in a deep cleft on the surface of each subunit, where one ATP molecule and one Mg(2+) are observed. A strictly conserved HXGH motif (in single-letter amino acid code) is involved in ATP binding and recognition.

CONCLUSIONS

The structure of NMN AT closely resembles that of phosphopantetheine adenylyltransferase. Remarkably, in spite of the fact that the two enzymes share the same fold and hexameric assembly, a striking difference in their quaternary structure is observed. Moreover, on the basis of structural similarity including the HXGH motif, we identify NMN AT as a novel member of the newly proposed superfamily of nucleotidyltransferase alpha/beta phosphodiesterases. Our structural data suggest that the catalytic mechanism does not rely on the direct involvement of any protein residues and is likely to be carried out through optimal positioning of substrates and transition-state stabilisation, as is proposed for other members of the nucleotidyltransferase alpha/beta phosphodiesterase superfamily.

Autonomic nervous system activity imbalance in cardiomyopathic hamster

There is strong evidence that autonomic imbalance plays an important role in progression of heart failure. Analysis of heart rate variability (HRV) has achieved substantial acceptance as a noninvasive method for the assessment of autonomic tone. The purpose of this investigation was to study HRV in an experimental model of heart failure using cardiomyopathic (BIO TO.2) hamsters. Animals showed an autonomic imbalance of cardiac control that seems due to attenuation of parasympathetic activity and an enhanced sympathetic tone. The reduction of parasympathetic activity in BIO TO.2 hamsters is suggested by (a) the reduction of the high-frequency (HF) spectrum, and (b) the lack of atropine to generate a response. The increased sympathetic activity is indicated by (a) the decreased time-domain indexes, (b) the increased LF/HF ratio of the power spectrum, and (c) the alteration of HRV indexes induced by propranolol. These results support the notion that in heart failure, there is a similar autonomic imbalance in both human and hamster and suggest that the cardiomyopathic hamster is a suitable experimental model for studying the involvement of the autonomic nervous system in the progression of heart failure.

Human erythrocyte pyrimidine 5-nucleotidase, PN-I, is identical to p36, a protein associated to lupus inclusion formation in response to alpha-interferon

Erythrocyte maturation is accompanied by RNA degradation and release of mononucleotides. We have previously purified PN-I, a pyrimidine nucleotidase whose deficiency is associated with hemolytic anemia. Computer-aided analysis of PN-I tryptic and CNBr peptide sequences revealed substantial identity with tryptic peptide sequences reported for p36, an alpha-interferon-induced protein. PN-I partial sequences were matched through the expressed sequence tag database with different human complementary DNA (cDNA) clones, whose sequences were exploited to screen a human placenta cDNA library. PN-I cDNA, coding for a 286-residue protein, was expressed in Escherichia coli, yielding a fully active recombinant enzyme. The recombinant protein sequence comprised the peptide sequences determined for PN-I and p36. Rabbit antisera raised against two peptides deriving from p36 and PN-I tryptic digestions, respectively, recognized both wild-type and recombinant PN-I. Molecular properties of the two proteins were essentially the same. We conclude that p36 and PN-I are identical proteins. (Blood. 2000;96:1596-1598)

Social adjustment in bipolar and unipolar single-episode and recurrently depressed inpatients

Social adjustment scores were compared using the Social Adjustment Scale for 24 inpatients with single-episode major depression, 72 with recurrent major depression, and 28 with bipolar disorder. There were no differences between the three groups either in overall score or on single scales.

A prospective randomized double-blinded controlled study of ropivacaine 0.75% versus bupivacaine 0.5%-mepivacaine 2% for peribulbar anesthesia

BACKGROUND AND OBJECTIVES

Ropivacaine 1% has recently been used in clinical trials for peribulbar anesthesia. This study aims to compare the safety and the efficacy of ropivacaine 0.75% with that of a 1:1 mixture of bupivacaine 0.5% and mepivacaine 2% for peribulbar anesthesia.

METHODS

Two thousand patients undergoing peribulbar anesthesia for elective cataract phacoemulsification were prospectively studied over a 1-year period and randomly assigned to 1 of 2 groups according to the local anesthetic used. One thousand patients were administered peribulbar anesthesia with 9 mL of ropivacaine 0.75% plus 1 mL of hyaluronidase (group R), and 1,000 patients received peribulbar anesthesia with 4 mL of bupivacaine 0.5% plus 4 mL of mepivacaine 2% plus 1 mL of hyaluronidase plus 1 mL of sodium bicarbonate (group BM). Peribulbar anesthesia was always accomplished by the same physician by 2 injections of 5 mL each, with a 25-gauge 25-mm needle. Evaluation was performed by another physician blinded to the technique used and included assessment of pain on local anesthetic injection, ocular and eyelid akinesia, need for top-up injections, onset time and duration of anesthesia, intraoperative analgesia, duration of surgery, hemodynamic parameters, and incidence of perioperative complications.

RESULTS

A greater incidence of pain on injection was found in group BM (P<.001). No difference between the groups was found regarding the onset time and the duration of anesthesia. Perioperative analgesia was satisfactory in both groups with no significant difference. Patients in group R showed a reduced need for top-up injection and a better ocular akinesia at 8 and 10 minutes (P<.01). The akinesia of the eyelid was comparable in the 2 groups and complete in all cases at 8 minutes. Cardiac arrhythmias were more frequent in group BM (P<.01). Local complications did not differ between the groups. An increase in mean artierial blood pressure and heart rate was observed in both groups 1 minute after injection of local anesthetic.

CONCLUSIONS

Peribulbar anesthesia with ropivacaine provided better ocular akinesia 8 to 10 minutes after block insertion than a bupivacaine-mepivacaine mixture, which reduced the need for top-up injections. Ropivacaine also caused less pain on injection.

The Escherichia coli NadR regulator is endowed with nicotinamide mononucleotide adenylyltransferase activity

The first identification and characterization of a catalytic activity associated with NadR protein is reported. A computer-aided search for sequence similarity revealed the presence in NadR of a 29-residue region highly conserved among known nicotinamide mononucleotide adenylyltransferases. The Escherichia coli nadR gene was cloned into a T7-based vector and overexpressed. In addition to functionally specific DNA binding properties, the homogeneous recombinant protein catalyzes NAD synthesis from nicotinamide mononucleotide and ATP.

Open study of the catechol-O-methyltransferase inhibitor tolcapone in major depressive disorder

Tolcapone is a catechol-O-methyltransferase (COMT) inhibitor that has shown efficacy in the treatment of Parkinson's disease. The authors undertook the first study on the efficacy of this COMT inhibitor in the treatment of major depressive disorder (MDD). The authors also wanted to assess the effects of tolcapone on the choline and myoinositol resonances in the left caudate and dorsolateral frontal lobe through proton magnetic resonance spectroscopy and on whole blood levels of S-adenosyl-L-methionine (SAMe). The study enrolled 21 adults (10 men and 11 women; mean age, 42.6 +/- 9.6 years) with MDD, which was diagnosed using the Structured Clinical Interview for DSM-IV, and an initial score of > or = 16 on the 17-item Hamilton Rating Scale for Depression (HAM-D-17). Patients were then treated openly for 8 weeks with tolcapone 400 mg twice daily. Treatment efficacy was assessed with the HAM-D-17, the Clinical Global Impressions Severity (CGI-S) scale, and the Beck Depression Inventory (BDI). Among all subjects (N = 21), there were significant (p < .0001) decreases at endpoint in HAM-D-17 scores (from 19.4 +/- 2.9 to 10.7 +/- 5.5), CGI-S scores (from 3.9 +/- 0.6 to 2.4 +/- 1.1), and BDI scores (from 21.6 +/- 8.1 to 12.3 +/- 8.6). Eight patients (38%) dropped out before completing the 8-week open study because of diarrhea, elevated liver function tests, increased anxiety, and noncompliance. No significant effects were noted on choline and myoinositol resonance or on SAMe levels in whole blood before and after 2 weeks of tolcapone treatment. The preliminary results suggest that tolcapone may be a promising agent in the treatment of MDD. Furthermore, double-blind, placebo-controlled studies are necessary to confirm this impression.

Identification and characterization of YLR328W, the Saccharomyces cerevisiae structural gene encoding NMN adenylyltransferase. Expression and characterization of the recombinant enzyme

The enzyme nicotinamide mononucleotide (NMN) adenylyltransferase (EC 2.7.7.1) catalyzes the transfer of the adenylyl moiety of ATP to NMN to form NAD. A new purification procedure for NMN adenylyltransferase from Saccharomyces cerevisiae provided sufficient amounts of enzyme for tryptic fragmentation. Through data-base search a full matching was found between the sequence of tryptic fragments and the sequence of a hypothetical protein encoded by the S. cerevisiae YLR328W open reading frame (GenBank accession number U20618). The YLR328W gene was isolated, cloned into a T7-based vector and successfully expressed in Escherichia coli BL21 cells, yielding a high level of NMN adenylyltransferase activity. The purification of recombinant protein, by a two-step chromatographic procedure, resulted in a single polypeptide of 48 kDa under SDS-PAGE, in agreement with the molecular mass of the hypothetical protein encoded by YLR328W ORF. The N-terminal sequence of the purified recombinant NMN adenylyltransferase exactly corresponds to the predicted sequence. Molecular and kinetic properties of recombinant NMN adenylyltransferase are reported and compared with those already known for the enzyme obtained from different sources.

Extrapyramidal symptoms associated with the adjunct of nortriptyline to a venlafaxine-valproic acid combination

The onset of extrapyramidal symptoms has been traditionally linked to the prescription of neuroleptic treatment: there are some reports in the international literature describing extrapyramidal effects related to antidepressant. In this paper we present a case under multiple pharmacologic treatment in whom extrapyramidal symptoms developed shortly after the adjunct of nortriptyline to a combination of venlafaxine and valproic acid administered for several months. We describe here the clinical history of this patient, affected by Bipolar Disorder, type II, and the progressive pharmacologic path in his treatment. Possible hypothesis to explain this evidence are discussed.

Enzymology of NAD+ synthesis

Beyond its role as an essential coenzyme in numerous oxidoreductase reactions as well as respiration, there is growing recognition that NAD+ fulfills many other vital regulatory functions both as a substrate and as an allosteric effector. This review describes the enzymes involved in pyridine nucleotide metabolism, starting with a detailed consideration of the anaerobic and aerobic pathways leading to quinolinate, a key precursor of NAD+. Conversion of quinolinate and 5'-phosphoribosyl-1'-pyrophosphate to NAD+ and diphosphate by phosphoribosyltransferase is then explored before proceeding to a discussion the molecular and kinetic properties of NMN adenylytransferase. The salient features of NAD+ synthetase as well as NAD+ kinase are likewise presented. The remainder of the review encompasses the metabolic steps devoted to (a) the salvaging of various niacin derivatives, including the roles played by NAD+ and NADH pyrophosphatases, nicotinamide deamidase, and NMN deamidase, and (b) utilization of niacins by nicotinate phosphoribosyltransferase and nicotinamide phosphoribosyltransferase.

Pyrimidine nucleotidases/phosphotransferases from human erythrocyte

Two cytoplasmic pyrimidine 5'-nucleotidase have been purified from human erythrocytes to homogeneity and partially characterized. The two enzymes, indicated as PN-I and PN-II, preferentially hydrolyse pyrimidine 5'-monophosphates and 3'-monophosphates, respectively. The kinetic analysis demonstrate that pyrimidine 5'-nucleotidases, in the presence of suitable nucleoside substrates, can operate as phosphotransferases by transferring phosphate to various nucleoside acceptors, including nucleoside analogues known as important drugs widely used in chemotherapy.