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The 2015 redesign of the Medical College Admissions Test (MCAT) is a disruptive event that has stimulated a great deal of discussion in undergraduate educational circles. These discussions include figuring out who will teach biochemistry, whether nonmajor chemistry courses should be changed, whether the psychosocial material to be tested constitutes academic behavioral science or the sensibilities that come from exposure to different cultures, and determining whether resources need to shift. The 2015 MCAT has also begun to alter admissions requirements and curricula in medical, pharmacy, and dental schools. Though many medical schools are taking the position that biochemistry will already have been covered as an undergraduate requirement and seem to be deemphasizing molecular science in the first-year curriculum, at least one college of dentistry has embraced the better prepared first-year student in order to offer advanced biochemistry and genomics that will build on undergraduate biochemistry. [ABSTRACT FROM AUTHOR]

Eukaryotic nicotinamide riboside kinase (Nrk) converts nicotinamide riboside to NAD+ by phosphorylation and adenylylation. The structures of this enzyme bound to several substrates lead to identification of new pathways to NAD+ [ABSTRACT FROM AUTHOR]

The article focuses on a enzyme that links two metabolic hubs in human body. It states that the enzyme has been found to be unregulated in the fat cells of overweight mice. It further states that the inhibition of the gene encoding this enzyme protects mice from diet-induced obesity. It further highlights that mice that lack or overexpress GLUT4 in fat are used as models for people sensitized to or resistant to diabetes.

We recently discovered that nicotinamide riboside, previously thought to be a bacterial NAD precursor, is a vitamin precursor of NAD in yeast and humans, which is converted to NAD in a pathway initiated by specific nicotinamide riboside kinases. Nicotinamide riboside has been shown to allow dorsal ganglion root neurons to resist axonopathy and the nicotinamide riboside kinase 2 gene has been shown to be induced by damage. In this study, we describe a second biosynthetic pathway for nicotinamide riboside salvage in yeast and human cells. We establish the conditions in which yeast cells take up the compound and convert it to NAD and we show that both of the newly identified nicotinamide riboside salvage pathways increase Sir2 activity in gene silencing and promote yeast cell longevity in the absence of calorie restriction. [ABSTRACT FROM AUTHOR]

NAD+ is an essential coenzyme for hydride transfer enzymes and a substrate of sirtuins and other NAD+-consuming enzymes. Nicotinamide riboside is a recently discovered eukaryotic NAD+ precursor converted to NAD+ via the nicotinamide riboside kinase pathway and by nucleosidase activity and nicotinamide salvage. Nicotinamide riboside supplementation of yeast extends replicative life span on high glucose medium. The molecular basis for nicotinamide riboside uptake was unknown in any eukaryote. Here, we show that deletion of a single gene, YOR071C, abrogates nicotinamide riboside uptake without altering nicotinic acid or nicotinamide import. The gene, which is negatively regulated by Sum!, Hst1, and Rfm1, fully restores nicotinamide riboside import and utilization when resupplied to mutant yeast cells. The encoded polypeptide, Nrt1, is a predicted deca-spanning membrane protein related to the thiamine transporter, which functions as a pH-dependent facilitator with a Km for nicotinamide riboside of 22 µM. Nrt1-related molecules are conserved in particular fungi, suggesting a similar basis for nicotinamide riboside uptake. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD+) is both a coenzyme for hydride-transfer enzymes and a substrate for NAD+-consuming enzymes, which include ADP-ribose transferases, poly(ADP-ribose) polymerases, cADP-ribose synthases and sirtuins. Recent results establish protective roles for NAD+ that might be applicable therapeutically to prevent neurodegenerative conditions and to fight Candida glabrata infection. In addition, the contribution that NAD+ metabolism makes to lifespan extension in model systems indicates that therapies to boost NAD+ might promote some of the beneficial effects of calorie restriction. Nicotinamide riboside, the recently discovered nucleoside precursor of NAD+ in eukaryotic systems, might have advantages as a therapy to elevate NAD+ without inhibiting sirtuins, which is associated with high-dose nicotinamide, or incurring the unpleasant side-effects of high-dose nicotinic acid. [Copyright &y& Elsevier]

Ataxia-oculomotor apraxia syndrome 1 is an early onset cerebellar ataxia that results from loss of function mutations in the APTX gene, encoding Aprataxin, which contains three conserved domains. The forkhead-associated domain of Aprataxin mediates protein-protein interactions with molecules that respond to DNA damage, but the cellular phenotype of the disease does not appear to be consistent with a major loss in DNA damage responses. Disease-associated mutations in Aprataxin target a histidine triad domain that is similar to Hint, a universally conserved AMP-lysine hydrolase, or truncate the protein NH2-terminal to a zinc finger. With novel fluorigenic substrates, we demonstrate that Aprataxin possesses an active-site-dependent AMP-lysine and GMP-lysine hydrolase activity that depends additionally on the zinc finger for protein stability and on the forkhead associated domain for enzymatic activity. Alleles carrying any of eight recessive mutations associated with ataxia and oculomotor apraxia encode proteins with huge losses in protein stability and enzymatic activity, consistent with a null phenotype. The mild presentation allele, APTX-K197Q, associated with ataxia but not oculomotor apraxia, encodes a protein with a mild defect in stability and activity, while enzyme encoded by the atypical presentation allele, APTXR199H, retained substantial function, consistent with altered and not loss of activity. The data suggest that the essential function of Aprataxin is reversal of nucleotidylylated protein modifications, that all three domains contribute to formation of a stable enzyme, and that the in vitro behavior of cloned APTX alleles can score disease-associated mutations. [ABSTRACT FROM AUTHOR]

Hint, histidine triad nucleotide-binding protein, is a universally conserved enzyme that hydrolyzes AMP linked to lysine and, in yeast, functions as a positive regulator of the RNA polymerase II C-terminal domain kinase, Kin28. To explore the biochemical and structural bases for the adenosine phosphoramidate hydrolase activity of rabbit Hint, we synthesized novel substrates linking a p-nitroaniline group to adenylate (AMP-pNA) and inhibitors that consist of an adenosine group and 5′-sulfamoyl (AdoOSO2NH2) or N-ethylsulfamoyl (AdoOSO2NHCH2CH3) group. AMP-pNA is a suitable substrate for Hint that allowed characterization of the inhibitors; titration of each inhibitor into AMP-pNA assays revealed their Ki values. The N-ethylsulfamoyl derivative has a 13-fold binding advantage over the sulfamoyl adenosine. The 1.8-Å cocrystal structure of rabbit Hint with N-ethylsulfamoyl adenosine revealed a binding site for the ethyl group against Trp-123, a residue that reaches across the Hint dimer interface to interact with the alkyl portion of the inhibitor and, presumably, the alkyl portion of a lysyl substrate. Ser-107 is positioned to donate a hydrogen bond to the leaving group nitrogen. Consistent with a role in acid-base catalysis, the Hint S107A mutant protein displayed depressed catalytic activity. [ABSTRACT FROM AUTHOR]

A novel human cytosolic flavin reductase, Nr1, was recently described that contains FMN, FAD, and NADPH cofactors. Though the targets of the related NADPH-dependent flavoprotein reductases, cytochrome P450 reductase, methionine synthase reductase, and nitric oxide synthase, are known, the cellular function of Nr1 is not clear. To explore expression and regulation of Nr1, we cloned fre-1, the Caenorhabditis elegans ortholog of Nr1, and dis- covered that it is transcribed as a bicistronic pre-mRNA together with dcs-1, the ortholog of the recently described scavenger mRNA decapping enzyme. We used the novel substrate, 7meGpppBODIPY, to demonstrate that DCS-1 has low micromolar specificity for guanine ribonucleotides with the 7me modification, whereas trimethylated G substrates are poor competitors. Contrary to earlier classification, DCS-1 is not a pyrophosphatase but a distant member of the Hint branch of the histidine triad superfamily of nucleotide hydrolases and transferases. These observations are consistent with the hypothesis that DCS-1 homologs may function in the metabolism of capped oligonucleotides generated following exosome-dependent degradation of short-lived mRNA transcripts. We find that fre-1 and dcs-1 are coordinately expressed through worm development, are induced by heat shock, and have a nearly identical expression profile in human tissues. Furthermore, immunocytochemical analysis of the endogenous proteins in COS cells indicates that both are present in the nucleus and concentrated in a distinct perinuclear structure. Though no connection between these enzymes had been anticipated, our data and data from global expression and protein association studies suggest that the two enzymes jointly participate in responses to DNA damage, heat shock, and other stresses. [ABSTRACT FROM AUTHOR]