Phosphoserine aminotransferase deficiency diagnosed by whole-exome sequencing and LC-MS/MS reanalysis: A case report and review of literature.

BACKGROUND: Phosphoserine aminotransferase deficiency (PSATD) is an autosomal recessive disorder associated with hypertonia, psychomotor retardation, and acquired microcephaly. Patients with PSATD have low concentrations of serine in plasma and cerebrospinal fluid. METHODS: We reported a 2-year-old female child with developmental delay, dyskinesia, and microcephaly. LC-MS/MS was used to detect amino acid concentration in the blood and whole-exome sequencing (WES) was used to identify the variants. PolyPhen-2 web server and PyMol were used to predict the pathogenicity and changes in the 3D model molecular structure of protein caused by variants. RESULTS: WES demonstrated compound heterozygous variants in PSAT1, which is associated with PSATD, with a paternal likely pathogenic variant (c.235G>A, Gly79Arg) and a maternal likely pathogenic variant (c.43G>C, Ala15Pro). Reduced serine concentration in LC-MS/MS further confirmed the diagnosis of PSATD in this patient. CONCLUSIONS: Our findings demonstrate the importance of WES combined with LC-MS/MS reanalysis in the diagnosis of genetic diseases and expand the PSAT1 variant spectrum in PSATD. Moreover, we summarize all the cases caused by PSAT1 variants in the literature. This case provides a vital reference for the diagnosis of future cases.

Dysregulated oxalate metabolism is a driver and therapeutic target in atherosclerosis.

Dysregulated glycine metabolism is emerging as a common denominator in cardiometabolic diseases, but its contribution to atherosclerosis remains unclear. In this study, we demonstrate impaired glycine-oxalate metabolism through alanine-glyoxylate aminotransferase (AGXT) in atherosclerosis. As found in patients with atherosclerosis, the glycine/oxalate ratio is decreased in atherosclerotic mice concomitant with suppression of AGXT. Agxt deletion in apolipoprotein E-deficient (Apoe-/-) mice decreases the glycine/oxalate ratio and increases atherosclerosis with induction of hepatic pro-atherogenic pathways, predominantly cytokine/chemokine signaling and dysregulated redox homeostasis. Consistently, circulating and aortic C-C motif chemokine ligand 5 (CCL5) and superoxide in lesional macrophages are increased. Similar findings are observed following dietary oxalate overload in Apoe-/- mice. In macrophages, oxalate induces mitochondrial dysfunction and superoxide accumulation, leading to increased CCL5. Conversely, AGXT overexpression in Apoe-/- mice increases the glycine/oxalate ratio and decreases aortic superoxide, CCL5, and atherosclerosis. Our findings uncover dysregulated oxalate metabolism via suppressed AGXT as a driver and therapeutic target in atherosclerosis.

Adult diagnosis of congenital serine biosynthesis defect: A treatable cause of progressive neuropathy.

A woman with ichthyosis, contractures, and progressive neuropathy represents the first case of phosphoserine aminotransferase deficiency diagnosed and treated in an adult. She has novel compound heterozygous mutations in the gene PSAT1. Treatment with high dose oral L-serine completely resolved the ichthyosis. Consideration of this diagnosis is important because early treatment with L-serine repletion can halt progression of neurodegeneration and potentially improve neurological disabilities. As exome sequencing becomes more widely implemented in the diagnostic evaluation of progressive neurodegenerative phenotypes, adult neurologists and geneticists will increasingly encounter later onset manifestations of inborn errors of metabolism classically considered in infancy and early childhood.

Exogenous and Endogenous Sources of Serine Contribute to Colon Cancer Metabolism, Growth, and Resistance to 5-Fluorouracil.

Serine is a nonessential amino acid generated by the sequential actions of phosphoglycerate dehydrogenase (PHGDH), phosphoserine aminotransferase (PSAT1), and phosphoserine phosphatase (PSPH). Increased serine biosynthesis occurs in several cancers and supports tumor growth. In addition, cancer cells can harness exogenous serine to enhance their metabolism and proliferation. Here we tested the relative contributions of exogenous and endogenous sources of serine on the biology of colorectal cancer. In murine tumors, Apc status was identified as a determinant of the expression of genes controlling serine synthesis. In patient samples, PSAT1 was overexpressed in both colorectal adenomas and adenocarcinomas. Combining genetic deletion of PSAT1 with exogenous serine deprivation maximally suppressed the proliferation of colorectal cancer cells and induced profound metabolic defects including diminished nucleotide production. Inhibition of serine synthesis enhanced the transcriptional changes following exogenous serine removal as well as alterations associated with DNA damage. Both loss of PSAT1 and removal of serine from the diet were necessary to suppress colorectal cancer xenograft growth and enhance the antitumor activity of 5-fluorouracil (5-FU). Restricting endogenous and exogenous serine in vitro augmented 5-FU-induced cell death, DNA damage, and metabolic perturbations, likely accounting for the observed antitumor effect. Collectively, our results suggest that both endogenous and exogenous sources of serine contribute to colorectal cancer growth and resistance to 5-FU. SIGNIFICANCE: These findings provide insights into the metabolic requirements of colorectal cancer and reveal a novel approach for its treatment. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/9/2275/F1.large.jpg.

Phosphoserine aminotransferase deficiency: imaging findings in a child with congenital microcephaly.

Serine deficiency disorders can result from deficiency in one of three enzymes. Deficiency of the second enzyme, 3-phosphoserine aminotransferase (PSAT), has been reported in two siblings; the eldest investigated for acquired microcephaly, spasticity and epilepsy. Our patient had neurological symptoms at birth. Fetal magnetic resonance imaging (MRI) at 35-week gestation demonstrated microencephaly and gyral simplification (anterior > posterior) which was confirmed upon postnatal MRI. Congenital microcephaly was apparent at birth. PSAT deficiency was confirmed when exome sequencing identified biallelic mutations in PSAT1 and biochemical testing noted low plasma serine and cerebral spinal fluid serine. Despite oral serine and glycine supplementation at 4 months old, the patient showed little neurodevelopmental progress and developed epileptic spasms at 10 months old. PSAT deficiency should be considered for patients with congenital microcephaly. Although further characterization of MRI findings in other patients is required, microencephaly with simplified gyral pattern could provide imaging clues for this rare metabolic disorder.

Depletion of branched-chain aminotransferase 2 (BCAT2) enzyme impairs myoblast survival and myotube formation.

Much is known about the positive effects of branched-chain amino acids (BCAA) in regulating muscle protein metabolism. Comparatively much less is known about the effects of these amino acids and their metabolites in regulating myotube formation. Using cultured myoblasts, we showed that although leucine is required for myotube formation, this requirement is easily met by α-ketoisocaproic acid, the ketoacid of leucine. We then demonstrated increases in the expression of the first two enzymes in the catabolism of the three BCAA, branched-chain amino transferase (BCAT2) and branched-chain α-ketoacid dehydrogenase (BCKD), with ~3× increase in BCKD protein expression (p < .05) during differentiation. Furthermore, depletion of BCAT2 abolished myoblast differentiation, as indicated by reduction in the levels of myosin heavy chain-1, troponin and myogenin. Supplementation of incubation medium with branched-chain α-ketoacids or related metabolites derivable from BCAT2 functions did not rescue the defects. However, co-depletion of BCKD kinase partially rescued the defects. Collectively, our data indicate a requirement for BCAA catabolism during myotube formation and that this requirement for BCAT2 likely goes beyond the need for this enzyme to generate the α-ketoacids of the BCAA.

Expanding the genetic and phenotypic spectrum of branched-chain amino acid transferase 2 deficiency.

The first step in branched-chain amino acid (BCAA) catabolism is catalyzed by the two BCAA transferase isoenzymes, cytoplasmic branched-chain amino acid transferase (BCAT) 1, and mitochondrial BCAT2. Defects in the second step of BCAA catabolism cause maple syrup urine disease (MSUD), a condition which has been far more extensively investigated. Here, we studied the consequences of BCAT2 deficiency, an ultra-rare condition in humans. We present genetic, clinical, and functional data in five individuals from four different families with homozygous or compound heterozygous BCAT2 mutations which were all detected following abnormal biochemical profile results or familial mutation segregation studies. We demonstrate that BCAT2 deficiency has a recognizable biochemical profile with raised plasma BCAAs and, in contrast with MSUD, low-normal branched-chain keto acids (BCKAs) with undetectable l-allo-isoleucine. Interestingly, unlike in MSUD, none of the individuals with BCAT2 deficiency developed acute encephalopathy even with exceptionally high BCAA levels. We observed wide-ranging clinical phenotypes in individuals with BCAT2 deficiency. While one adult was apparently asymptomatic, three individuals had presented with developmental delay and autistic features. We show that the biochemical characteristics of BCAT2 deficiency may be amenable to protein-restricted diet and that early treatment may improve outcome in affected individuals. BCAT2 deficiency is an inborn error of BCAA catabolism. At present, it is unclear whether developmental delay and autism are parts of the variable phenotypic spectrum of this condition or coincidental. Further studies will be required to explore this.

Generation of a Primary Hyperoxaluria Type 1 Disease Model Via CRISPR/Cas9 System in Rats.

BACKGROUND: Primary hyperoxaluria type 1 (PH1) is an inherited disease caused by mutations in alanine-glyoxylate aminotransferase (AGXT). It is characterized by abnormal metabolism of glyoxylic acid in the liver leading to endogenous oxalate overproduction and deposition of oxalate in multiple organs, mainly the kidney. Patients of PH1 often suffer from recurrent urinary tract stones, and finally renal failure. There is no effective treatment other than combined liver-kidney transplantation. METHODS: Microinjection was administered to PH1 rats. Urine samples were collected for urine analysis. Kidney tissues were for Western blotting, quantitative PCR, AGT assays and histological evaluation. RESULTS: In this study, we generated a novel PH1 disease model through CRISPR/Cas9 mediated disruption of mitochondrial localized Agxt gene isoform in rats. Agxt-deficient rats excreted more oxalate in the urine than WT animals. Meanwhile, mutant rats exhibited crystalluria and showed a slight dilatation of renal tubules with mild fibrosis in the kidney. When supplied with 0.4% ethylene glycol (EG) in drinking water, mutant rats excreted greater abundance of oxalate and developed severe nephrocalcinosis in contrast to WT animals. Significantly elevated expression of inflammation- and fibrosisrelated genes was also detected in mutants. CONCLUSION: These data suggest that Agxt-deficiency in mitochondria impairs glyoxylic acid metabolism and leads to PH1 in rats. This rat strain would not only be a useful model for the study of the pathogenesis and pathology of PH1 but also a valuable tool for the development and evaluation of innovative drugs and therapeutics.

Disturbed phospholipid metabolism in serine biosynthesis defects revealed by metabolomic profiling.

Serine biosynthesis defects are autosomal recessive metabolic disorders resulting from the deficiency of any of the three enzymes involved in de novo serine biosynthesis, specifically phosphoglycerate dehydrogenase (PGDH), phosphoserine aminotransferase (PSAT), and phosphoserine phosphatase (PSP). In this study, we performed metabolomic profiling on 4 children with serine biosynthesis defects; 3 with PGDH deficiency and 1 with PSAT deficiency. The evaluations were performed at baseline and with serine and glycine supplementation. Metabolomic profiling performed at baseline showed low phospholipid species, including glycerophosphocholine, glycerophosphoethanolamine, and sphingomyelin. All children had low serine and glycine as expected. Low glycerophosphocholine compounds were found in 4 children, low glycerophosphoethanolamine compounds in 3 children, and low sphingomyelin species in 2 children. Metabolic profiling with serine and glycine supplementation showed normalization of most of the low phospholipid compounds in the 4 children. Phospholipids are the major component of plasma and intracellular membranes, and phosphatidylcholine is the most abundant phospholipid of all mammalian cell types and subcellular organelles. Phosphatidylcholine is of particular importance for the nervous system, where it is essential for neuronal differentiation. The observed low phosphatidylcholine species in children with serine biosynthesis defects that improved after serine supplementation, supports the role of serine as a significant precursor for phosphatidylcholine. The vital role that phosphatidylcholine has during neuronal differentiation and the pronounced neurological manifestations in serine biosynthesis defects suggest that phosphatidylcholine deficiency occurring secondary to serine deficiency may have a significant contribution to the development of the neurological manifestations in individuals with serine biosynthesis defects.

Correlation between the molecular effects of mutations at the dimer interface of alanine-glyoxylate aminotransferase leading to primary hyperoxaluria type I and the cellular response to vitamin B6.

Primary hyperoxaluria type I (PH1) is a rare disease caused by the deficit of liver alanine-glyoxylate aminotransferase (AGT). AGT prevents oxalate formation by converting peroxisomal glyoxylate to glycine. When the enzyme is deficient, progressive calcium oxalate stones deposit first in the urinary tract and then at the systemic level. Pyridoxal 5'-phosphate (PLP), the AGT coenzyme, exerts a chaperone role by promoting dimerization, as demonstrated by studies at protein and cellular level. Thus, variants showing a destabilized dimeric structure should, in principle, be responsive to vitamin B6, a precursor of PLP. However, models to predict the extent of responsiveness of each variant are missing. We examined the effects of pathogenic interfacial mutations by combining bioinformatic predictions with molecular and cellular studies on selected variants (R36H, G42E, I56N, G63R, and G216R), in both their holo- (i.e., with bound PLP) and apo- (i.e., without bound PLP) form. We found that all variants displayed structural alterations mainly related to the apoform and consisting of an altered tertiary and quaternary structure. G216R also shows a strongly reduced catalytic efficiency. Moreover, all but G216R respond to vitamin B6, as shown by their increased specific activity and expression level in a cellular disease model. A global analysis of data unraveled a possible inverse correlation between the degree of destabilization/misfolding induced by a mutation and the extent of B6 responsiveness. These results provide a first explanation of factors influencing B6 response in PH1, a model possibly valuable for other rare diseases caused by protein deficits.

Natural Variation in SER1 and ENA6 Underlie Condition-Specific Growth Defects in Saccharomyces cerevisiae.

Despite their ubiquitous use in laboratory strains, naturally occurring loss-of-function mutations in genes encoding core metabolic enzymes are relatively rare in wild isolates of Saccharomyces cerevisiae Here, we identify a naturally occurring serine auxotrophy in a sake brewing strain from Japan. Through a cross with a honey wine (white tecc) brewing strain from Ethiopia, we map the minimal medium growth defect to SER1, which encodes 3-phosphoserine aminotransferase and is orthologous to the human disease gene, PSAT1 To investigate the impact of this polymorphism under conditions of abundant external nutrients, we examine growth in rich medium alone or with additional stresses, including the drugs caffeine and rapamycin and relatively high concentrations of copper, salt, and ethanol. Consistent with studies that found widespread effects of different auxotrophies on RNA expression patterns in rich media, we find that the SER1 loss-of-function allele dominates the quantitative trait locus (QTL) landscape under many of these conditions, with a notable exacerbation of the effect in the presence of rapamycin and caffeine. We also identify a major-effect QTL associated with growth on salt that maps to the gene encoding the sodium exporter, ENA6 We demonstrate that the salt phenotype is largely driven by variation in the ENA6 promoter, which harbors a deletion that removes binding sites for the Mig1 and Nrg1 transcriptional repressors. Thus, our results identify natural variation associated with both coding and regulatory regions of the genome that underlie strong growth phenotypes.

BCAT1 restricts αKG levels in AML stem cells leading to IDHmut-like DNA hypermethylation.

The branched-chain amino acid (BCAA) pathway and high levels of BCAA transaminase 1 (BCAT1) have recently been associated with aggressiveness in several cancer entities. However, the mechanistic role of BCAT1 in this process remains largely uncertain. Here, by performing high-resolution proteomic analysis of human acute myeloid leukaemia (AML) stem-cell and non-stem-cell populations, we find the BCAA pathway enriched and BCAT1 protein and transcripts overexpressed in leukaemia stem cells. We show that BCAT1, which transfers α-amino groups from BCAAs to α-ketoglutarate (αKG), is a critical regulator of intracellular αKG homeostasis. Further to its role in the tricarboxylic acid cycle, αKG is an essential cofactor for αKG-dependent dioxygenases such as Egl-9 family hypoxia inducible factor 1 (EGLN1) and the ten-eleven translocation (TET) family of DNA demethylases. Knockdown of BCAT1 in leukaemia cells caused accumulation of αKG, leading to EGLN1-mediated HIF1α protein degradation. This resulted in a growth and survival defect and abrogated leukaemia-initiating potential. By contrast, overexpression of BCAT1 in leukaemia cells decreased intracellular αKG levels and caused DNA hypermethylation through altered TET activity. AML with high levels of BCAT1 (BCAT1high) displayed a DNA hypermethylation phenotype similar to cases carrying a mutant isocitrate dehydrogenase (IDHmut), in which TET2 is inhibited by the oncometabolite 2-hydroxyglutarate. High levels of BCAT1 strongly correlate with shorter overall survival in IDHWTTET2WT, but not IDHmut or TET2mut AML. Gene sets characteristic for IDHmut AML were enriched in samples from patients with an IDHWTTET2WTBCAT1high status. BCAT1high AML showed robust enrichment for leukaemia stem-cell signatures, and paired sample analysis showed a significant increase in BCAT1 levels upon disease relapse. In summary, by limiting intracellular αKG, BCAT1 links BCAA catabolism to HIF1α stability and regulation of the epigenomic landscape, mimicking the effects of IDH mutations. Our results suggest the BCAA-BCAT1-αKG pathway as a therapeutic target to compromise leukaemia stem-cell function in patients with IDHWTTET2WT AML.

Cancer progression by reprogrammed BCAA metabolism in myeloid leukaemia.

Reprogrammed cellular metabolism is a common characteristic observed in various cancers. However, whether metabolic changes directly regulate cancer development and progression remains poorly understood. Here we show that BCAT1, a cytosolic aminotransferase for branched-chain amino acids (BCAAs), is aberrantly activated and functionally required for chronic myeloid leukaemia (CML) in humans and in mouse models of CML. BCAT1 is upregulated during progression of CML and promotes BCAA production in leukaemia cells by aminating the branched-chain keto acids. Blocking BCAT1 gene expression or enzymatic activity induces cellular differentiation and impairs the propagation of blast crisis CML both in vitro and in vivo. Stable-isotope tracer experiments combined with nuclear magnetic resonance-based metabolic analysis demonstrate the intracellular production of BCAAs by BCAT1. Direct supplementation with BCAAs ameliorates the defects caused by BCAT1 knockdown, indicating that BCAT1 exerts its oncogenic function through BCAA production in blast crisis CML cells. Importantly, BCAT1 expression not only is activated in human blast crisis CML and de novo acute myeloid leukaemia, but also predicts disease outcome in patients. As an upstream regulator of BCAT1 expression, we identified Musashi2 (MSI2), an oncogenic RNA binding protein that is required for blast crisis CML. MSI2 is physically associated with the BCAT1 transcript and positively regulates its protein expression in leukaemia. Taken together, this work reveals that altered BCAA metabolism activated through the MSI2-BCAT1 axis drives cancer progression in myeloid leukaemia.

Primary hyperoxaluria in an adult male: A rare cause of end-stage kidney disease yet potentially fatal if misdiagnosed.

Primary hyperoxaluria is an autosomal recessive disorder due to a deficiency in the activity of the peroxisomal hepatic enzyme alanine-glyoxylate aminotransferase. It is a common cause of urolithiasis and end-stage kidney disease in children contrary to the adult phenotypic presentation which is considered a mild disorder with occasional urolithiasis. In this case report, we describe a 25-year-old man who presented with advanced and irreversible kidney failure within three months following strenuous physical training in the police academy. He had nephrocalcinosis and stones in one kidney. Diagnosis was confirmed by establishing the existence of extensive tubular and interstitial crystal deposition in his kidneys and molecular genetic testing. The case illustrates the need to establish an early diagnosis of this disorder to prevent the need for combined liver and kidney transplantation.

Two new cases of serine deficiency disorders treated with l-serine.

OBJECTIVE AND PATIENTS: We report on two new cases of serine deficiency due respectively to 3-phosphoglycerate dehydrogenase (PHGDH) deficiency (Patient 1) and phosphoserine aminotransferase (PSAT1) deficiency (Patient 2), presenting with congenital microcephaly (<3rd centile at birth) and encephalopathy with spasticity. Patient 1 had also intractable seizures. A treatment with oral l-serine was started at age 4.5 years and 3 months respectively. RESULTS: Serine levels were low in plasma and CSF relative to the reference population, for which we confirm recently redefined intervals based on a larger number of samples. l-Serine treatment led in patient 1 to a significant reduction of seizures after one week of treatment and decrease of electroencephalographic abnormalities within one year. In patient 2 treatment with l-serine led to an improvement of spasticity. However for both patients, l-serine failed to improve substantially head circumference (HC) and neurocognitive development. In a couple related to patient's 2 family, dosage of serine was performed on fetal cord blood when the fetus presented severe microcephaly, showing reduced serine levels at 30 weeks of pregnancy. CONCLUSIONS: l-Serine treatment in patients with 2 different serine synthesis defects, led to a significant reduction of seizures and an improvement of spasticity, but failed to improve substantially neurocognitive impairment. Therefore, CSF and plasma serine levels should be measured in all cases of severe microcephaly at birth to screen for serine deficiency, as prompt treatment with l-serine may significantly impact the outcome of the disease. Reduced serine levels in fetal cord blood may also be diagnostic as early as 30 weeks of pregnancy.

Glycolate Oxidase Is a Safe and Efficient Target for Substrate Reduction Therapy in a Mouse Model of Primary Hyperoxaluria Type I.

Primary hyperoxaluria type 1 (PH1) is caused by deficient alanine-glyoxylate aminotransferase, the human peroxisomal enzyme that detoxifies glyoxylate. Glycolate is one of the best-known substrates leading to glyoxylate production, via peroxisomal glycolate oxidase (GO). Using genetically modified mice, we herein report GO as a safe and efficient target for substrate reduction therapy (SRT) in PH1. We first generated a GO-deficient mouse (Hao1(-/-)) that presented high urine glycolate levels but no additional phenotype. Next, we produced double KO mice (Agxt1(-/-) Hao1(-/-)) that showed low levels of oxalate excretion compared with hyperoxaluric mice model (Agxt1(-/-)). Previous studies have identified some GO inhibitors, such as 4-carboxy-5-[(4-chlorophenyl)sulfanyl]-1,2,3-thiadiazole (CCPST). We herein report that CCPST inhibits GO in Agxt1(-/-) hepatocytes and significantly reduces their oxalate production, starting at 25 µM. We also tested the ability of orally administered CCPST to reduce oxalate excretion in Agxt1(-/-) mice, showing that 30-50% reduction in urine oxalate can be achieved. In summary, we present proof-of-concept evidence for SRT in PH1. These encouraging results should be followed by a medicinal chemistry programme that might yield more potent GO inhibitors and eventually could result in a pharmacological treatment for this rare and severe inborn error of metabolism.

SNP Variants in RET and PAX2 and Their Possible Contribution to the Primary Hyperoxaluria Type 1 Phenotype.

Primary hyperoxaluria type 1 (PH1) is a rare genetic kidney disease caused by a deficiency of alanine:glyoxylate aminotransferase (AGT). Genetic heterogeneity of the AGT gene cannot fully account for heterogeneity in the clinical phenotype. This study investigates a possible contribution to the clinical phenotype from SNPs in RET or PAX2 genes associated with reduced nephron number. The frequencies of these SNPs were compared in PH1-affected DNA samples and normal controls, and relative to age of onset in PH1-affected individuals. The frequencies of the risk alleles were higher with early age of onset, although not significantly so. However, homozygosity for the risk alleles of RET and PAX2 was not seen in the late onset group. The overall frequencies of risk alleles and the numbers of homozygotes were significantly higher for PAX2 in PH1 samples versus controls, suggestive of a bias towards more severe clinical phenotypes in the PH1 samples submitted for analysis.

Decreased production of higher alcohols by Saccharomyces cerevisiae for Chinese rice wine fermentation by deletion of Bat aminotransferases.

An appropriate level of higher alcohols produced by yeast during the fermentation is one of the most important factors influencing Chinese rice wine quality. In this study, BAT1 and BAT2 single- and double-gene-deletion mutant strains were constructed from an industrial yeast strain RY1 to decrease higher alcohols during Chinese rice wine fermentation. The results showed that the BAT2 single-gene-deletion mutant strain produced best improvement in the production of higher alcohols while remaining showed normal growth and fermentation characteristics. Furthermore, a BAT2 single-gene-deletion diploid engineered strain RY1-Δbat2 was constructed and produced low levels of isobutanol and isoamylol (isoamyl alcohol and active amyl alcohol) in simulated fermentation of Chinese rice wine, 92.40 and 303.31 mg/L, respectively, which were 33.00 and 14.20 % lower than those of the parental strain RY1. The differences in fermentation performance between RY1-Δbat2 and RY1 were minor. Therefore, construction of this yeast strain is important in future development in Chinese wine industry and provides insights on generating yeast strains for other fermented alcoholic beverages.

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

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.

Effect of cofactor folate on the growth of Corynebacterium glutamicum SYPS-062 and L-serine accumulation.

The direct fermentative production of L-serine from sugar has attracted increasing attention. Corynebacterium glutamicum SYPS-062 can directly convert sugar to L-serine. In this study, the effects of exogenous and endogenous regulation of cofactor folate on C. glutamicum SYPS-062 growth and L-serine accumulation were investigated. For exogenous regulation, the inhibitor (sulfamethoxazole) or precursor (p-aminobenzoate) of folate biosynthesis was added to the medium, respectively. For endogenous regulation, the gene (pabAB) that encodes the key enzyme of folate biosynthesis was knocked out or overexpressed to obtain the recombinant C. glutamicum SYPS-062 ΔpabAB and SYPS-062(pJC-tac-pabAB), respectively. The results indicated that decreased levels of cofactor folate supported L-serine accumulation, whereas increased levels of cofactor folate aided in cell growth of C. glutamicum SYPS-062. Thus, this study not only elucidated the role of folate in C. glutamicum SYPS-062 growth and L-serine accumulation, but also provided a novel and convenient approach to regulate folate biosynthesis in C. glutamicum.