Molecular cloning of a cDNA for human pyruvate carboxylase. Structural relationship to other biotin-containing carboxylases and regulation of mRNA content in differentiating preadipocytes

Clinical, biochemical, and molecular profiles of three Sri Lankan neonates with pyruvate carboxylase deficiency

Objectives

Pyruvate carboxylase, a mitochondrial enzyme, catalyses the conversion of glycolytic end-product pyruvate to tricarboxylic acid cycle intermediate, oxaloacetate. Rare pyruvate carboxylase deficiency manifests in three clinical and biochemical phenotypes: neonatal onset type A, infantile onset type B and a benign C type. The objective of this case series is to expand the knowledge of overlapping clinical and biochemical phenotypes of pyruvate carboxylase deficiency.

Case presentation

We report three Sri Lankan neonates including two siblings, of two unrelated families with pyruvate carboxylase deficiency. All three developed respiratory distress within the first few hours of birth. Two siblings displayed typical biochemical findings reported in type B. The other proband with normal citrulline, lysine, moderate lactate, paraventricular cystic lesions, bony deformities, and a novel missense, homozygous variant c.2746G>C [p.(Asp916His)] in the PC gene, biochemically favoured type A.

Conclusions

Our findings indicate the necessity of prompt laboratory investigations in a tachypneic neonate with coexisting metabolic acidosis, as early recognition is essential for patient management and family counselling. Further case studies are required to identify overlapping symptoms and biochemical findings in different types of pyruvate carboxylase deficiency phenotypes.

Perfiles clínicos, bioquímicos y moleculares de tres neonatos de Sri Lanka con déficit de piruvato carboxilasa

Objetivos

La piruvato carboxilasa (PC), una enzima mitocondrial, cataliza la conversión de piruvato, producto final de la glucólisis, en oxaloacetato, un intermediario del ciclo del ácido tricarboxílico. El déficit de piruvato carboxilasa, un trastorno raro, se manifiesta en tres fenotipos clínicos y bioquímicos: tipo de inicio neonatal (tipo A), tipo de inicio infantil (tipo B) y un tipo benigno (tipo C).

Caso clínico

Presentamos el caso de tres neonatos de Sri Lanka, incluidos dos hermanos, de dos familias no emparentadas, con déficit de piruvato carboxilasa (DPC). Los tres desarrollaron dificultad respiratoria en las primeras horas de vida. Los dos hermanos presentaron las alteraciones bioquímicas típicas del tipo B. El tercer neonato presentaba niveles normales de citrulina y lisina, niveles moderados de lactato, lesiones quísticas paraventriculares, deformidades óseas y una nueva variante homocigótica sin sentido c.2746G>C [p.(Asp916His)] en el gen PC , indicativos bioquímicos de DPC tipo A.

Conclusiones

Nuestros hallazgos indican la urgencia de realizar estudios analíticos en los neonatos que presenten taquipnea con acidosis metabólica concomitante, dado que la identificación temprana es crucial para el manejo del paciente y la prestación de consejo genético a la familia. Son necesarios más estudios para identificar los síntomas y alteraciones bioquímicas concurrentes en los diferentes fenotipos de déficit de piruvato carboxilasa.

Disorders of pyruvate metabolism

Pyruvate dehydrogenase and pyruvate carboxylase deficiency are the most common disorders in pyruvate metabolism. Diagnosis is made by enzymatic and DNA analysis after basic biochemical tests in plasma, urine, and CSF. Pyruvate dehydrogenase has three main subunits, an additional E3-binding protein and two complex regulatory enzymes. Most frequent are deficiencies in PDH-E1α. There is a spectrum of clinical presentations in E1α deficiency, ranging in boys from severe neonatal lactic acidosis, Leigh encephalopathy, to later onset of neurological disease such as intermittent ataxia or dystonia. Females tend to have a more uniform presentation resembling nonprogressive cerebral palsy. Neuroradiological abnormalities such as corpus callosum agenesis are seen more frequently in girls, basal ganglia and midbrain disturbances in boys. Deficiencies in the other subunits have also been described, but in a smaller number of patients. Pyruvate carboxylase deficiency has three clinical phenotypes. The infantile type is characterized mainly by severe developmental delay, failure to thrive, and seizures. The second type is characterized by neonatal onset of severe lactic acidosis with rigidity and hypokinesia. A third form is rarer with intermittent episodes of lactic acidosis and ketoacidosis. Neuroradiological findings such as cystic periventricular leukomalacia have been described.

The molecular basis of pyruvate carboxylase deficiency: mosaicism correlates with prolonged survival

Pyruvate carboxylase (PC) deficiency (OMIM, 266150) is a rare autosomal recessive disease. The revised PC gene structure described in this report consists of 20 coding exons and four non-coding exons at the 5'-untranslated region (5'-UTR). The gene codes for three transcripts due to alternative splicing: variant 1 (NM_000920.3), variant 2 (NM_022172.2) and variant 3 (BC011617.2). PC deficiency is manifested by three clinical phenotypes-an infantile form (Type A), a neonatal form (Type B), and a benign form (Type C). We report the molecular basis for eight cases (one Type A, five Type B and two Type C) of PC deficiency. Eight novel complex mutations were identified representing different combinations of missense mutations, deletions, a splice site substitution and a nonsense mutation. The classical phenotypes (A, B and C) correlated poorly with clinical outcomes. Mosaicism was found in five cases (one Type A, three Type B and one Type C) and four of these cases had prolonged survival. Death in the fifth case resulted from unrelated medical complications. The discrepancy between the current findings and the existing classification system should be addressed to accommodate these new observations.

Cloning of bovine pyruvate carboxylase and 5' untranslated region variants

Bovine pyruvate carboxylase (PC; EC 6.4.1.1) cDNA was cloned by reverse transcription (RT) PCR. The coding region plus 3' untranslated region (UTR) of PC mRNA is 3926 bases and encodes 1178 amino acid PC precursor protein. A 5' rapid amplification of cDNA ends protocol was used to clone the 5' end of the mRNA. Six 5'UTR variants ranging from 68 to 363 bp were cloned. Bovine PC 5'UTR (bPC5') variants contain 68 (bPC5'A), 263 (bPC5'B), 363 (bPC5'C), 89 (bPC5'D), 275 (bPC5'E), and 178 bp (bPC5'F). All variants contain a common coding sequence. An RNase protection assay and RT-PCR analysis confirms the presence of the 5'UTR variants. The abundance of PC mRNA, determined by Northern blot analysis, indicates that PC is more abundant in gluconeogenic and lipogenic tissues where all PC variants are expressed compared with tissues that do not possess the full spectrum of PC transcripts. The data suggest that bPC5'A, bPC5'B, and bPC5'F are more abundant in bovine liver than the other variants.

Glucose/mitochondria in neurological conditions

Impairments of glucose and mitochondrial function are important causes of brain dysfunction and therefore of brain disease. Abnormalities have been found in association with disease of the nervous system in most of the components of glucose/mitochondrial metabolism. In many, molecular genetic abnormalities have been defined. Brain glucose oxidation is abnormal in common diseases of the nervous system, including Alzheimer disease and other dementias, Parkinson disease, delirium, probably schizophrenia and other psychoses, and of course cerebrovascular disease. Defects in a single component and even a single mutation can be associated with different clinical phenotypes. The same clinical phenotype can result from different genotypes. The complex relationship between biological abnormality in brain glucose utilization and clinical disorder is similar to that in other disorders that have been intensively studied at the genetic level. Genes for components of the pathways of brain glucose oxidation are good candidate genes for disease of the brain. Preliminary data support the proposal that treatments to normalize abnormalities in brain glucose oxidation may benefit many patients with common brain diseases.

The molecular basis of human 3-methylcrotonyl-CoA carboxylase deficiency

Isolated biotin-resistant 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder of leucine catabolism that appears to be the most frequent organic aciduria detected in tandem mass spectrometry-based neonatal screening programs. The phenotype is variable, ranging from neonatal onset with severe neurological involvement to asymptomatic adults. MCC is a heteromeric mitochondrial enzyme composed of biotin-containing alpha subunits and smaller beta subunits. Here, we report cloning of MCCA and MCCB cDNAs and the organization of their structural genes. We show that a series of 14 MCC-deficient probands defines two complementation groups, CG1 and 2, resulting from mutations in MCCB and MCCA, respectively. We identify five MCCA and nine MCCB mutant alleles and show that missense mutations in each result in loss of function.

Cloning, sequencing, and expression of the pyruvate carboxylase gene in Lactococcus lactis subsp. lactis C2

A functional pyc gene was isolated from Lactococcus lactis subsp. lactis C2 and was found to complement a Pyc defect in L. lactis KB4. The deduced lactococcal Pyc protein was highly homologous to Pyc sequences of other bacteria. The pyc gene was also detected in Lactococcus lactis subsp. cremoris and L. lactis subsp. lactis bv. diacetylactis strains.

Regulation of rat pyruvate carboxylase gene expression by alternate promoters during development, in genetically obese rats and in insulin-secreting cells. Multiple transcripts with 5'-end heterogeneity modulate translation

A previous study on the gene structure of rat pyruvate carboxylase revealed that two tissue-specific promoters are responsible for the production of multiple transcripts with 5'-end heterogeneity (Jitrapakdee, S., Booker, G. W., Cassady, A. I., and Wallace, J. C. (1997) J. Biol. Chem. 272, 20522-20530). Here we report transcription and translation regulation of pyruvate carboxylase (PC) expression during development and in genetically obese rats. The abundance of PC mRNAs was low in fetal liver but increased by 2-4-fold within 7 days after birth, concomitant with an 8-fold increase in the amount of immunoreactive PC and its activity and then decreased during the weaning period. Reverse transcriptase polymerase chain reaction analysis indicated that the proximal promoter was activated during the suckling period and reduced in activity at weaning. In genetically obese Zucker rats, adipose PC was 4-5-fold increased, concomitant with a 5-6-fold increase in mRNA level. Reverse transcriptase-polymerase chain reaction analysis also showed that the proximal promoter was activated in the hyperlipogenic condition. Conversely, transcription of the proximal promoter was not detectable in various liver cell lines, suggesting that this promoter was not functional under cell culture conditions. In rat pancreatic islets and insulinoma cells, only transcripts D and E, generated from the distal promoter of the PC gene, were expressed. Glucose increased PC transcripts from the distal promoter when the insulinoma cells were maintained in 10 mM glucose. We conclude that the proximal promoter of the rat PC gene plays a major role in gluconeogenesis and lipogenesis, whereas the distal promoter is necessary for anaplerosis. In vitro translation and in vivo polysome profile analysis indicated that transcripts C and E were translated with similar translational efficiencies that are substantially greater than that of transcript D, suggesting that 5'-untranslated regions play a role in translational control.

Amerindian pyruvate carboxylase deficiency is associated with two distinct missense mutations

We characterized the pyruvate carboxylase (PC) gene by PCR amplification, subcloning, and sequencing. The coding region has 19 exons and 18 introns spanning approximately 16 kb of genomic DNA. Screening both the cDNA and the gene of individuals with the simple A form of PC deficiency revealed an 1828G-->A missense mutation in 11 Ojibwa and 2 Cree patients and a 2229G-->T transversion mutation in 2 brothers of Micmac origin. Carrier frequency may be as high as 1/10 in some groupings. The two point mutations are located in a region of homology conserved among yeast, rat, and human PC, in the vicinity of the carboxylation domain of the enzyme. These data provide the first characterization of the human PC gene structure, the identification of common pathogenic mutations, and the demonstration of a founder effect in the Ojibwa and Cree patients.

Molecular characterization of pyruvate carboxylase deficiency in two consanguineous families

Pyruvate carboxylase (PC) is a biotinylated mitochondrial enzyme that catalyzes the conversion of pyruvate to oxaloacetate. Children with inborn errors of PC metabolism have lactic acidosis, hypoglycemia, and mental retardation. The variable severity of the clinical phenotype is dependent on both genetic and environmental factors. Two consanguineous families with moderate forms of PC deficiency were characterized at the biochemical and molecular levels. In both families, the probands were found to have low PC activity (range, 2-25% of control) in blood lymphocytes and skin fibroblasts associated with either diminished or normal protein levels. In the first case, sequencing of patient-specific PC cDNA demonstrated a T to C substitution at nucleotide 434, which causes a valine to alanine change at amino acid residue 145. Direct sequencing of the parents showed that they are heterozygous for this mutation. In the second family, a brother and sister had mental retardation and episodes of severe lactic/ketoacidosis in early childhood. In these cases, a C to T substitution at nucleotide 1351 results in a cysteine for arginine substitution at amino acid residue 451; the parents were also found to be heterozygous for this mutation. In both families, no other mutations were found, and both substitutions occurred in relatively conserved amino acid residues. These mutations, located in the biotin carboxylase domain, provide a unique opportunity to analyze how natural occurring mutations affect PC function.

The rat pyruvate carboxylase gene structure. Alternate promoters generate multiple transcripts with the 5'-end heterogeneity

Pyruvate carboxylase (EC 6.4.1.1) is a biotin-containing enzyme that plays an important role in gluconeogenesis and lipogenesis. Here we report the structural organization of the rat pyruvate carboxylase gene, which spans over 40 kilobases and is composed of 19 coding exons and 4 5'-untranslated region exons. From this data, it is clear that alternative splicing of the primary transcripts from two promoters is responsible for the occurrence of the multiple mRNA species previously reported (Jitrapakdee, S., Walker, M. E., and Wallace, J. C. (1996) Biochem. Biophys. Res. Commun. 223, 695-700). The proximal promoter, which is active in gluconeogenic and lipogenic tissues, contains no TATA or CAAT boxes but includes a sequence that is typical of a housekeeping initiator protein 1 box while the distal promoter contains three CAAT boxes and multiple Sp1 binding sites. Several potential transcription factor binding sites are found in both promoters. A series of 5'-nested deletion constructs of both promoters were fused to a firefly luciferase reporter plasmid and transiently expressed in COS-1 cells. The results show that the 153 and 187 base pairs, preceding the transcription start sites of the proximal and distal promoters, respectively, are required for basal transcription. Insulin selectively inhibits the expression of the proximal promoter-luciferase reporter gene by 50% but not the distal promoter in COS-1 cells, suggesting the presence of an insulin-responsive element in the proximal promoter. A half-maximal effect was found at approximately 1 nM insulin.

A 3-Mb contig from D11S987 to MLK3, a gene-rich region in 11q13

We have combined genetic, radiation-reduced somatic cell hybrid (RRH), fluorescent in situ hybridization (FISH), and physical mapping methods to generate a contig of overlapping YAC, PAC, and cosmid clones corresponding to > 3 continuous Mb in 11q13. A total of 15 STSs [7 genes (GSTP1, ACTN, PC, MLK3, FRA1, SEA, HNP36), 4 polymorphic loci (D11S807, D11S987, GSTP1, D11S913), 3 ESTs (D11S1956E, D11S951E, and W1-12191), and 1 anonymous STS (D11S703)], mapping to three independent RRH segregation groups, identified 26 YAC, 7 PAC, and 16 cosmid clones from the CGM, Roswell Park, CEPH Mark I, and CEPH MegaYAC YAC libraries, a 5 genome equivalent PAC library, and a chromosome II-specific cosmid library. Thirty-six Alu-PCR products derived from 10 anonymous bacteriophage lambda clones, a cosmid containing the polymorphic marker D11S460, or STS-positive YAC or cosmid clones were identified and used to screen selected libraries by hybridization, resulting in the identification of 19 additional clones. The integrity and relative position of a subset of clones was confirmed by FISH and were found to be consistent with the physical and RRH mapping results. The combination of STS and Alu-PCR-based approaches has proven to be successful in attaining contiguous cloned coverage in this very GC-rich region, thereby establishing for the first time the absolute order and distance between the markers: CEN-MLK3-(D11S1956E/D11S951E/W1-12191)-FRA1-D 11S460-SEA-HNP36/ D11S913-ACTN-PC-D11S703-GSTP1-D11S987-TEL.

The structure and the mechanism of action of pyruvate carboxylase

Pyruvate carboxylase plays an important role in intermediary metabolism, catalysing the formation of oxaloacetate from pyruvate and HCO3-, with concomitant ATP cleavage. It thus provides oxaloacetate for gluconeogenesis and replenishing tricarboxylic acid cycle intermediates for fatty acid, amino acid and neurotransmitter synthesis. The enzyme is highly conserved and is found in a great variety of organisms including fungi, bacteria and plants as well as higher organisms. It is a member of a group of biotin-dependent enzymes and the biotin prosthetic group is covalently bound to the polypeptide chain of the enzyme, there normally being four such chains in the native, tetrameric enzyme. The overall reaction catalysed by pyruvate carboxylase involves two partial reactions that occur at spatially separate subsites within the active site, with the covalently bound biotin acting as a mobile carboxyl group carrier. In the first partial reaction, biotin is carboxylated using ATP and HCO3- as substrates whilst in the second partial reaction, the carboxyl group from carboxybiotin is transferred to pyruvate. The chemical mechanisms of the partial reactions and some of the roles played by amino acid residues of the enzyme in catalysing the reaction have been elucidated. The domain structure of the yeast enzyme has been deduced by comparing its amino acid sequence with those of enzymes that have similar catalytic functions. The quaternary structures of the pyruvate carboxylases studied so far, all involve a tetrahedron-like arrangement of the subunits. The major regulator of enzyme activity, acetyl CoA, stimulates the cleavage of ATP in the first partial reaction and in addition it has been shown to induce a conformational change in the tetrameric structure of the enzyme. In the past, the lack of any detailed structural information on the enzyme has hampered efforts to fully understand how this and other biotin-dependent enzymes function and are regulated. With the recent cloning of the enzyme from a variety of sources and the performance of three-dimensional structural studies, the next few years should see much progress in our understanding the mechanism of action of this enzyme.

Primary amino acid sequence and structure of human pyruvate carboxylase

Pyruvate carboxylase (PC) (pyruvate:carbon dioxide ligase (ADP-forming), EC 6.4.1.1.), a nuclear-encoded mitochondrial enzyme, catalyzes the conversion of pyruvate to oxaloacetate. We have isolated and characterized cDNAs spanning the entire coding region of human PC. The sequence of human PC has an open reading frame of 3537 nucleotides which encodes for a polypeptide with a length of 1178 amino acids. The identity of the cDNA as PC is confirmed by comparison to PC cDNAs of other species and sequenced peptide fragments of mammalian PC. The M(r) of the full length precursor protein is 129,576 and that of the mature apoprotein is 127,370. RNA blot analysis from a variety of human tissues demonstrates that the highest level of PC mRNA is found in liver corresponding to this tissue's high level of PC activity. Based on homology with other biotin-containing proteins, the ATP, pyruvate, and biotin-binding sites can be identified. One of two patients with documented PC deficiency was found to be missing PC mRNA, further confirming the identity of this cDNA.

A linkage map of mouse chromosome 19: definition of comparative mapping relationships with human chromosomes 10 and 11 including the MEN1 locus

A linkage map of mouse Chromosome (Chr) 19 was constructed using an interspecific cross and markers defined by restriction fragment length variants. The map includes 20 markers, 9 of which had not been mapped previously in the mouse. The data further defined the relationship between genes on mouse Chr 19 and those on the long arm of human Chr 10 and the pericentric region of the long arm of human Chr 11. The comparative mapping analysis suggests that the proximal segment of mouse Chr 19 may contain the MEN1 locus and that the current study has identified additional genes that may be useful for positional cloning of this putative tumor suppressor gene.

Variations in the relative amounts of biotin-containing enzymes present in both tumorigenic and non-tumorigenic hybrid cells and other cell lines

The observation that radioactively labelled streptavidin binds to several biotin-containing enzymes in mammalian cells has led to the finding that there is considerable variation in the proportion of these enzymes present (namely beta-methyl crotonyl CoA; propionyl CoA; pyruvate and acetyl CoA, carboxylases). This is particularly striking when certain tumorigenic and non-tumorigenic hybrid cells are compared. It is found that there is a consistently higher proportion of pyruvate carboxylase in the tumorigenic hybrid cells. However, not all tumorigenic cell lines show this same characteristic and reasons for this are discussed. It is also shown that whilst the proportions of the four enzymes are apparently constant for a given cell type, there is a substantial degree of clonal variation and this is particularly so in tumorigenic cells in vitro. However, the more tumorigenic cells in a given population do show a higher proportion of pyruvate carboxylase. Also a range of cells derived from lymphoid tissue has been compared with normal human lymphocytes and considerable differences are again observed. The significance of these findings is considered in relation to other phenotypic properties of hybrid cells.

Lactic acidosis and mitochondrial disorders

Characterization of the biochemical basis of various inherited disorders associated with lactic acidosis has increased dramatically in recent years. These include defects of enzymes of gluconeogenesis, pyruvate oxidation, and electron transport. Clinical manifestations of these disorders show great variation and overlap, frequently involving the central nervous system as well as skeletal and cardiac muscle. Several of these enzymes are large complexes of subunits encoded by multiple genes; the electron transport chain complexes include subunits encoded by both nuclear and mitochondrial genes. This great complexity complicates analysis of specific mutations, despite considerable progress in defining the primary structure of component proteins and their genes. With few exceptions, treatment of disorders associated with congenital lactic acidosis remains unsatisfactory.

Alterations of hepatic acetyl-CoA carboxylase by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on acetyl-CoA carboxylase (ACC) activity and synthesis was examined. Male Wistar rats received a single i.p. injection of TCDD (53 micrograms/kg), and nine days later body weight, liver weight, hepatic lipid, ACC activity and mass were determined and compared to pair-fed controls. Body weights of TCDD-treated animals decreased, while liver weights increased resulting in an increase in liver to body weight ratios. ACC activity was decreased by 65%, however sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western analysis using a biotin specific probe revealed that ACC protein levels were not appreciably changed. In addition, there was a large increase in exogenous lipid material in TCDD-treated livers as determined by osmium tetroxide staining. These data suggest that the decrease in ACC activity may be due to direct inhibition of the enzyme by negative allosteric interactions with free fatty acids released from adipose tissue that subsequently accumulate in liver.

The urea amidolyase (DUR1,2) gene of Saccharomyces cerevisiae

The DNA sequence of the urea amidolyase (DUR1,2) gene from S. cerevisiae has been determined. The polypeptide structure deduced from the DNA sequence contains 1,835 amino acid residues and possesses a calculated weight of 201,665 daltons which favorably correlates with that predicted from compositional analysis of purified protein (1,881 amino acid residues and a molecular weight of 203,900). The C-terminal 57 residues of the polypeptide exhibit significant homology with similarly situated sequences found in five other biotin carboxylases whose primary structures have been determined or deduced from protein and DNA sequence data, respectively. Major S1 nuclease protection fragments derived from DUR1,2 RNA-DNA hybrids exhibit apparent termini at positions -140 and -141 upstream of the coding region. The termini of minor protection fragments also occur at eleven other positions as well.

Simultaneous isolation of total cellular RNA and DNA from tissue culture cells using phenol and lithium chloride

A rapid procedure for the isolation of intact total cellular RNA from cultured cells is described. This method combines the simultaneous disruption of cells and extraction of nucleic acids in a single step with the use of phenol and a buffer containing 100 mM LiCl. Total cellular RNA can be isolated in approximately 2 hours. The yield and quality of the RNA is comparable to the more widely employed methods requiring extensive preparatory steps such as extraction using guanidinium thiocyanate and subsequent CsCl gradient centrifugation. The RNA isolated using our procedure contains transcripts up to 10 kb in length and is suitable for Northern analysis. This procedure also yields high-molecular-weight DNA, which is a suitable substrate for restriction endonucleases.

Analysis of the biotin-binding site on acetyl-CoA carboxylase from rat

The biotin-binding site of acetyl-CoA carboxylase from rat was characterized as to its amino acid sequence and relative position in the enzyme molecule. Biotin binds to the lysyl residue in the tetrapeptide Val-Met-Lys-Met; this tetrapeptide is located in close proximity to the NH2 terminus. In all other biotin-containing enzymes, the conserved tetrapeptide Ala-Met-Lys-Met is the counterpart to that of rat acetyl-CoA carboxylase; and the lysyl residue is 35 residues from the COOH terminus. To examine the significance of these unusual features of the biotinylation site of animal acetyl-CoA carboxylase, cDNA fragments were expressed in a bacterial system and the effects of specific site-directed mutagenesis were examined. Replacement of Val by Ala in the conserved tetrapeptide abolished biotinylation of the expressed protein. However, introduction of a termination codon at residue 36, in such a way that the distance between the lysine on which biotin binds and the COOH-terminal amino acid was 35 residues and the penultimate amino acid was the hydrophobic residue leucine, increased the efficiency of biotinylation, provided a substantial portion of the NH2-terminal peptide was removed.

Regulation of gene expression by insulin in adipose cells: opposite effects on adipsin and glycerophosphate dehydrogenase genes

Insulin is known to play the role of a positive effector both in vitro on the adipose conversion process and in vivo on the fatty acid synthesis and esterification processes in adipose tissue. The effects of insulin on the expression of two genes activated during adipose conversion, glycerol-3-phosphate dehydrogenase (GPDH) and adipsin genes, have been investigated in 3T3 F442A adipose cells. Within a physiological range of concentrations, insulin exerts opposite effects on the levels of GPDH (EC50 approximately 0.2 nM) and adipsin (EC50 approximately 1 nM) mRNAs. Its negative effect on the abundance of adipsin mRNA involves primarily a rapid inhibition of the transcriptional rate (less than 2 h). Its positive effect on the abundance of GPDH mRNA is due to a stimulation of the transcriptional rate accompanied by a delayed stabilization of GPDH mRNA. In addition, insulin exerts a specific effect on the length of the poly(A) tract of the adipsin mRNA. These results show that a single mechanism for the regulation of adipose-related genes by insulin can be excluded but rather suggest a complex phenomenon in which various levels of regulation take place.

A rapid purification method for rat liver pyruvate carboxylase and amino acid sequence analyses of NH2-terminal and biotin peptide

A rapid method for the purification of pyruvate carboxylase from rat liver has been developed. The method involves extraction of the enzyme from frozen liver powder followed by polyethylene glycol fractionation and avidin-affinity chromatography. The purified enzyme has a specific activity of 9-10 mumol/min/mg protein when assayed at 22 degrees C in the presence of acetyl-CoA. Polyacrylamide gel electrophoresis of the preparation in the presence of sodium dodecyl sulfate showed the presence of one protein band with an estimated Mr 125,000 and no significant contamination by other biotin-containing enzymes. In addition to being rapid, the method is advantageous because prior isolation of mitochondria is not necessary. Using these preparations we have determined the sequence of the first 15 amino acids from the NH2-terminal end of the molecule to be Ser-Gly-Pro-Val-Ala-Pro-Leu-Asn-Val-Leu-Leu-Leu-Glu-Tyr-Pro. The sequence of the 24 amino acid residues around the biotin site was determined to be Gly-Ala-Pro-Leu-Val-Leu-Ser-Ala-Met-biocytin-Met-Glu-Thr-Val-Val-Thr-Ser -Pro- Thr-Glu-Gly-Thr-Ile-Arg.

Pyruvate carboxylase in the yeast pyc mutant

Pyruvate carboxylase deficiency was previously reported to be the biochemical lesion in a yeast mutant, designated pyc, which cannot utilize ethanol, acetate, pyruvate, aspartate, or oxaloacetate as the sole carbon source [C. Wills and T. Melham (1985) Arch. Biochem. Biophys. 236, 782-791; C. Wills et al. (1986) Arch. Biochem. Biophys. 246, 306-320]. We present evidence here that the level of pyruvate carboxylase activity as well as the native and subunit molecular weights of this enzyme are identical in the mutant and the wild type. In addition we have used immunocytochemical labeling to demonstrate the exclusively cytosolic localization of this enzyme in both the mutant and wild-type yeast.

Yeast pyruvate carboxylase: gene isolation

To improve our understanding of pyruvate carboxylase (PC)(EC 6.4.1.1) structure and the evolution of the biotin-dependent carboxylases we have isolated and sequenced a yeast (Saccharomyces cerevisiae) genomic DNA fragment encoding PC. The identity of the cloned gene was confirmed by comparing the encoded protein with the sequence of a 26 amino acid biotin-containing peptide isolated from yeast PC. The yeast PC sequence is homologous (43% amino acid homology) to the rat PC sequence, although the carboxyl-terminus was found to be 44 residues from the biotinyl-lysine whereas in all biotin carboxylases sequenced to date the biotin is 35 residues from the carboxyl-terminus.

Sequence homology around the biotin-binding site of human propionyl-CoA carboxylase and pyruvate carboxylase

Biotin-dependent carboxylases require covalently bound biotin for enzymatic activity. The biotin is attached through a lysine residue, which in a number of bacterial, avian, and mammalian carboxylases, is found within the conserved sequence Ala-Met-Lys-Met. We have determined the partial nucleotide sequence of cDNA clones for human propionyl-CoA carboxylase and pyruvate carboxylase. The predicted amino acid sequence of both these proteins contains the conserved tetrapeptide 35 residues from the carboxy terminus. In addition, both proteins contain the tripeptide, Pro-Met-Pro, 26 residues toward the amino terminus from the biotin attachment site. The overall amino acid homology through this region is 43%. Similar findings have been made for the biotin-containing polypeptides of transcarboxylase of Propionibacterium shermanii and acetyl-CoA carboxylase of Escherichia coli (W. L. Maloy, B. U. Bowien, G. K. Zwolinski, K. G. Kumar, and H. G. Wood (1979) J. Biol. Chem. 254, 11615-11622). The implications of this sequence conservation with regard to the function and evolution of biotin-dependent carboxylases is discussed. We propose that the 60 amino acids surrounding the biotin site are bounded by a proline "hinge" and the carboxy terminus has remained conserved as a result of constraints imposed by biotinylation of the enzyme.

Primary structure of the biotin-binding site of chicken liver acetyl-CoA carboxylase

Limited proteolysis of chicken liver acetyl-CoA carboxylase by staphylococcal serine proteinase yielded a fragment of 31 kDa which contained the biotinyl active site. This polypeptide was purified by preparative polyacrylamide gel electrophoresis and characterized. The complete amino acid sequence of this polypeptide has been deduced from the nucleotide sequence of cloned DNA complementary to the chicken liver acetyl-CoA carboxylase mRNA. A highly conserved sequence of Met-Lys-Met was found in the biotin-binding site. Appreciable homology was observed among the sequences in close vicinity of the biotin sites of chicken liver acetyl-CoA carboxylase and other biotin-dependent carboxylases including biotin carboxyl carrier protein of Escherichia coli acetyl-CoA carboxylase.

The beta-subunit of follicle-stimulating hormone is deleted in patients with aniridia and Wilms' tumour, allowing a further definition of the WAGR locus

One in 10,000 children develops Wilms' tumour, an embryonal malignancy of the kidney. Although most Wilms' tumours are sporadic, a genetic predisposition is associated with aniridia, genito-urinary malformations and mental retardation (the WAGR syndrome). Patients with this syndrome typically exhibit constitutional deletions involving band p13 of one chromosome 11 homologue. It is likely that these deletions overlap a cluster of separate but closely linked genes that control the development of the kidney, iris and urogenital tract (the WAGR complex). A discrete aniridia locus, in particular, has been defined within this chromosomal segment by a reciprocal translocation, transmitted through three generations, which interrupts 11p13. In addition, the specific loss of chromosome 11p alleles in sporadic Wilms' tumours has been demonstrated, suggesting that the WAGR complex includes a recessive oncogene, analogous to the retinoblastoma locus on chromosome 13. In WAGR patients, the inherited 11p deletion is thought to represent the first of two events required for the initiation of a Wilms' tumour, as suggested by Knudson from epidemiological data. We have now isolated the deleted chromosomes 11 from four WAGR patients in hamster-human somatic cell hybrids, and have tested genomic DNA from the hybrids with chromosome 11-specific probes. We show that 4 of 31 markers are deleted in at least one patient, but that of these markers, only the gene encoding the beta-subunit of follicle-stimulating hormone (FSHB) is deleted in all four patients. Our results demonstrate close physical linkage between FSHB and the WAGR locus, suggest a gene order for the four deleted markers and exclude other markers tested from this region. In hybrids prepared from a balanced translocation carrier with familial aniridia, the four markers segregate into proximal and distal groups. The translocation breakpoint, which identifies the position of the aniridia gene on 11p, is immediately proximal to FSHB, in the interval between FSHB and the catalase gene.