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Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by defects in enzymes of the L-serine biosynthesis pathway.

ABSTRACT: Neu-Laxova syndrome (NLS) is a rare autosomal-recessive disorder characterized by a recognizable pattern of severe malformations leading to prenatal or early postnatal lethality. Homozygous mutations in PHGDH, a gene involved in the first and limiting step in L-serine biosynthesis, were recently identified as the cause of the disease in three families. By studying a cohort of 12 unrelated families affected by NLS, we provide evidence that NLS is genetically heterogeneous and can be caused by mutations in all three genes encoding enzymes of the L-serine biosynthesis pathway. Consistent with recently reported findings, we could identify PHGDH missense mutations in three unrelated families of our cohort. Furthermore, we mapped an overlapping homozygous chromosome 9 region containing PSAT1 in four consanguineous families. This gene encodes phosphoserine aminotransferase, the enzyme for the second step in L-serine biosynthesis. We identified six families with three different missense and frameshift PSAT1 mutations fully segregating with the disease. In another family, we discovered a homozygous frameshift mutation in PSPH, the gene encoding phosphoserine phosphatase, which catalyzes the last step of L-serine biosynthesis. Interestingly, all three identified genes have been previously implicated in serine-deficiency disorders, characterized by variable neurological manifestations. Our findings expand our understanding of NLS as a disorder of the L-serine biosynthesis pathway and suggest that NLS represents the severe end of serine-deficiency disorders, demonstrating that certain complex syndromes characterized by early lethality could indeed be the extreme end of the phenotypic spectrum of already known disorders.

SUBMITTER: Acuna-Hidalgo R

PROVIDER: S-EPMC4157144 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by defects in enzymes of the L-serine biosynthesis pathway.

Acuna-Hidalgo Rocio R Schanze Denny D Kariminejad Ariana A Nordgren Ann A Kariminejad Mohamad Hasan MH Conner Peter P Grigelioniene Giedre G Nilsson Daniel D Nordenskjöld Magnus M Wedell Anna A Freyer Christoph C Wredenberg Anna A Wieczorek Dagmar D Gillessen-Kaesbach Gabriele G Kayserili Hülya H Elcioglu Nursel N Ghaderi-Sohi Siavash S Goodarzi Payman P Setayesh Hamidreza H van de Vorst Maartje M Steehouwer Marloes M Pfundt Rolph R Krabichler Birgit B Curry Cynthia C MacKenzie Malcolm G MG Boycott Kym M KM Gilissen Christian C Janecke Andreas R AR Hoischen Alexander A Zenker Martin M

American journal of human genetics 20140821 3

Neu-Laxova syndrome (NLS) is a rare autosomal-recessive disorder characterized by a recognizable pattern of severe malformations leading to prenatal or early postnatal lethality. Homozygous mutations in PHGDH, a gene involved in the first and limiting step in L-serine biosynthesis, were recently identified as the cause of the disease in three families. By studying a cohort of 12 unrelated families affected by NLS, we provide evidence that NLS is genetically heterogeneous and can be caused by mut ...[more]

PMID: 25152457

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Project description:We report the results of an investigation into the catalytic role of highly conserved amide (asparagine, glutamine) and OH-containing (serine, tyrosine) residues in several prenyltransferases. We first obtained the X-ray structure of cyclolavandulyl diphosphate synthase containing two molecules of the substrate analog dimethylallyl (S)-thiolodiphosphate (DMASPP). The two molecules have similar diphosphate group orientations to those seen in other ζ-fold (cis- head-to-tail and head-to-middle) prenyltransferases with one diphosphate moiety forming a bidentate chelate with Mg2+ in the so-called S1 site (which is typically the allylic binding site in ζ-fold proteins) while the second diphosphate binds to Mg2+ in the so-called S2 site (which is typically the homoallylic binding site in ζ-fold proteins) via a single P1O1 oxygen. The latter interaction can facilitate direct phosphate-mediated proton abstraction via P1O2, or more likely by an indirect mechanism in which P1O2 stabilizes a basic asparagine species that removes H+, which is then eliminated via an Asn-Ser shuttle. The universal occurrence of Asn-Ser pairs in ζ-fold proteins leads to the idea that the highly conserved amide (Asn, Gln) and OH-containing (Tyr) residues seen in many "head-to-head" prenyltransferases such as squalene and dehydrosqualene synthase might play similar roles, in H+ elimination. Structural, bioinformatics and mutagenesis investigations indeed indicate an important role of these residues in catalysis, with the results of density functional theory calculations showing that Asn bound to Mg2+ can act as a general (imine-like) base, while Gln, Tyr and H2O form a proton channel that is adjacent to the conventional (Asp-rich) "active site". Taken together, our results lead to mechanisms of proton-elimination from carbocations in numerous prenyltransferases in which neutral species (Asn, Gln, Ser, Tyr, H2O) act as proton shuttles, complementing the more familiar roles of acidic groups (in Asp and Glu) that bind to Mg2+, and basic groups (primarily Arg) that bind to diphosphates, in isoprenoid biosynthesis.

Project description:Malic enzymes decarboxylate the tricarboxylic acid (TCA) cycle intermediate malate to the glycolytic end-product pyruvate and are well positioned to regulate metabolic flux in central carbon metabolism. The bacterium Sinorhizobium meliloti has a NAD(P)-malic enzyme (DME) and a NADP-malic enzyme (TME) and DME is required for symbiotic N2-fixation. To help understand the role of these enzymes, we examined growth, metabolic and transcriptional consequences resulting from the deletion of these enzymes. Few effects were observed upon growth with glucose, whereas growth with the gluconeogenic substrate, succinate, resulted in transcriptional and metabolic effects particularly in the dme mutant strains. When grown with succinate, DME mutant cells accumulated hexose sugar phosphates and trehalose, while TME mutants accumulated putrescine. Succinate-grown DME mutant cells also showed increased transcription of genes for gluconeogenesis and for pathways such as amino acid and fatty acid synthesis that divert metabolites away from the TCA cycle. These data suggested that, DME is required to regulate the levels of TCA cycle intermediates and that the activity of TME is insufficient to prevent the accumulation of TCA cycle intermediates in cells utilizing succinate as carbon source. Consistent with this, in short-1-3 hour incubations with succinate, dme mutant cells excreted large amounts of malate whereas little malate was excreted from tme or wild-type cells. These results support the suggestion that DME is required for N2-fixation in alfalfa because it is required for synthesis of pyruvate and acetyl-CoA and the rapid metabolism of C4-dicarboxylates supplied by the plant. RNA expression was measured for S. meliloti in exponential phase grown in MOPS (morpholinpropanesulfonic acid) buffered minimal media under 2 growth conditions: 1) 15 mM succinate, 2) 15 mM glucose; using wild type cells as well as dme and tme mutant strains (6 experiments, 2 replicates: total 12 samples)

Dataset Information

Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by defects in enzymes of the L-serine biosynthesis pathway.

Publications

Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by defects in enzymes of the L-serine biosynthesis pathway.

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