Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We studied a large number of individuals with respect to the 31-bp variable number tandem repeat (VNTR) in the cystathionine beta-synthase (CBS) gene. The number of repeats varies from 15-20, with 17 repeats the most common allele. Significantly, we found that the first repeat of the 31-bp VNTR originates 12 bp from the 5' end of exon 13 and extends 19 bp into intron 13. Since this VNTR spans across the exon-intron border, it can theoretically create multiple alternate splice sites. However, a substitution of g-->a at the exon-intron border is uniquely present in the second repeat, preventing alternate splicing at that site. While the g-->a substitution is absent from all subsequent 31-bp repeats, alternate splicing probably does not occur at those distal sites due to the lack of exon 13 sequences not contained in the repeats but needed for the binding of spliceosomes. Investigation of five individuals with normal plasma total homocysteine (tHcy) and five individuals with mild hyper-homocysteinemia shows that all have the g-->a substitution in the second repeat. Nonetheless, we speculate that the absence of this substitution may be found in rare individuals with normal CBS cDNA and unexplained hyperhomocysteinemia. Gene scanning and direct nucleotide sequencing were used to characterize the VNTR in 398 patients with premature coronary artery disease and 137 controls. Five alleles and 10 genotypes were found; 17/17 is the most prevalent genotype in our study population. The two other prevalent genotypes, 16/17 and 17/18, are associated with significantly decreased tHcy levels as compared to the 17/ 17 genotype, suggesting that the 16 and 18 repeats haplotype may be in linkage disequilibrium with regulatory elements which upregulate CBS gene transcription.
Am J Med Genet 2000 Dec 11
PMID:Variable number tandem repeat in exon/intron border of the cystathionine beta-synthase gene: a single nucleotide substitution in the second repeat prevents multiple alternate splicing. 1118 95

The nucleotide sequence of a 4,539 bp fragment of Bacillus stearothermophilus V mediating tellurite resistance in Escherichia coli was determined. Four ORFs of more than 150 amino acids encoding polypeptides of 244, 258, 308, and 421 residues were found in the restriction fragment. E. coli cells harboring a recombinant plasmid containing the Ter determinant express, when challenged with tellurite, a 32 kDa protein with an amino terminal sequence identical to the ten first residues of the 308 ORF. This ORF shows great similarity with the cysteine synthase gene (cysK) of a number of organisms. Recombinant clones carrying the active cysK gene have minimal inhibitory concentrations to K2TeO3 that were tenfold higher than those determined for the host strain or that of clones carrying ORFs 244, 258, and 421. Introduction of the B. stearothermophilus V cysK gene into a cysK strain of Salmonella typhimurium LT2 resulted in complementation of the mutation as well as transfer of tellurite resistance.
Curr Microbiol 2001 Dec
PMID:The product of the cysK gene of Bacillus stearothermophilus V mediates potassium tellurite resistance in Escherichia coli. 1168 9

An inborn error of metabolism, homocystinuria due to cystathionine beta-synthase deficiency, results in markedly elevated levels of circulating homocysteine. Premature vascular events are the main life-threatening complication. Half of all untreated patients have a vascular event by 30 years of age. We performed a multicenter observational study to assess the effectiveness of long-term homocysteine-lowering treatment in reducing vascular risk in 158 patients. Vascular outcomes were analyzed and effectiveness of treatment in reducing vascular risk was evaluated by comparison of actual to predicted number of vascular events, with the use of historical controls from a landmark study of 629 untreated patients with cystathionine beta-synthase deficiency. The 158 patients had a mean (range) age of 29.4 (4.5 to 70) years; 57 (36%) were more than 30 years old, and 10 (6%) were older than 50 years. There were 2822 patient-years of treatment, with an average of 17.9 years per patient. Plasma homocysteine levels were markedly reduced from pretreatment levels but usually remained moderately elevated. There were 17 vascular events in 12 patients at a mean (range) age of 42.5 (18 to 67) years: pulmonary embolism (n=3), myocardial infarction (n=2), deep venous thrombosis (n=5), cerebrovascular accident (n=3), transient ischemic attack (n=1), sagittal sinus thrombosis (n=1), and abdominal aortic aneurysm (n=2). Without treatment, 112 vascular events would have been expected, for a relative risk of 0.09 (95% CI 0.036 to 0.228; P<0.0001). Treatment regimens designed to lower plasma homocysteine significantly reduce cardiovascular risk in cystathionine beta-synthase deficiency despite imperfect biochemical control. These findings may be relevant to the significance of mild hyperhomocysteinemia that is commonly found in patients with vascular disease.
Arterioscler Thromb Vasc Biol 2001 Dec
PMID:Vascular outcome in patients with homocystinuria due to cystathionine beta-synthase deficiency treated chronically: a multicenter observational study. 1174 88

Homocysteine is a key junction metabolite that can be converted to cystathionine in a reaction catalyzed by the heme and pyridoxal phosphate-dependent cystathionine beta-synthase. The heme has unusual spectroscopic properties and the axial ligands have been assigned as histidine and cysteine, respectively. Its role in the protein is not obvious from the chemistry of the beta-replacement reaction that is catalyzed. We have characterized the binding of the gaseous signaling molecule, NO, to cystathionine beta-synthase and examined its effect on the reactions catalyzed by the truncated dimeric form of the enzyme, W409X, which is a natural variant. Binding of NO appears to result in the formation of a five-coordinate ferrous nitrosyl species in which both endogenous ligands have been lost. This is in contrast to CO binding which is reported to displace the thiolate ligand and form a six-coordinate species. NO binds to the full-length enzyme with a K(d) of 281+/-50 microM and to the truncated enzyme with a K(d) of 350+/-44 microM. Binding of NO to the full-length enzyme inhibits activity with a K(i) of 320+/-60 microM. These studies demonstrate that as with CO, perturbation of the heme environment by NO is communicated to the active site with concomitant inhibition of enzyme activity, and suggests a regulatory role for heme in cystathionine beta-synthase.
J Inorg Biochem 2001 Dec 15
PMID:Characterization of NO binding to human cystathionine beta-synthase: possible implications of the effects of CO and NO binding to the human enzyme. 1174 62

Cystathionine beta-synthase is a key heme and pyridoxal phosphate-dependent enzyme involved in homocysteine metabolism in humans. The role of the recently discovered heme in this protein remains an important open question. The axial ligands to the heme in both the ferrous and ferric states have been assigned as cysteine and histidine residues, respectively. In this study, we have examined the effect of ligation and spin state changes in the heme on the activity of the enzyme. Treatment of the ferric enzyme with HgCl2 results in the conversion of six-coordinate low-spin heme to five-coordinate high-spin heme and is paralleled by a loss of activity. In contrast, treatment of the ferrous enzyme with HgCl2 results in replacement of the cysteine ligand by an unidentified sixth ligand and retention of the six-coordinate state, and is also accompanied by loss of enzyme activity. Treatment of the five-coordinate HgCl2-treated enzyme with thiols, such as homocysteine, results in reversion to a six-coordinate state. Resonance Raman spectroscopy with 34S-labeled enzyme reveals the return of the endogenous thiol ligand under these conditions and rules out direct coordination by the thiolate of homocysteine to the heme.
J Inorg Biochem 2001 Dec 15
PMID:Mercuric chloride-induced spin or ligation state changes in ferric or ferrous human cystathionine beta-synthase inhibit enzyme activity. 1174 63

Recent reports suggested that homocystinuria due to cystathionine beta-synthase (CBS) deficiency is a more common inborn error of metabolism than originally thought. In this study we compared the prevalence of homocystinuric alleles ascertained by two different approaches. First, the incidence of homocystinuria estimated by selective biochemical screening in the Czech and Slovak Republics was 1:349,000 (95% CI 1:208,000-1:641,000). The two most common pathogenic mutant alleles found subsequently in these patients, IVS11-2A>C and c.833T>C, had a calculated population prevalence of 0.00042 (95% CI 0.00031-0.00055) and 0.00018 (95% CI 0.00013-0.00023), respectively. Second, to examine the possible negative detection bias of mildly affected patients we determined the prevalence of these two pathogenic mutations in a sample of 1284 unselected newborns. Indeed, the observed prevalence of the c.833T>C allele (0.00195, 95% CI 0.00063-0.00454) was 11x higher than in the previous group suggesting that many homozygotes for the c.833T>C had not been diagnosed by selective biochemical screening. The IVS11-2A>C allele was not detected among 2,568 newborn CBS alleles. The estimated incidence of homocystinuria of 1:83,000, calculated in a combined model, suggests that selective biochemical screening may ascertain only approximately 25% of all homocystinuric patients. In conclusion, homocystinuria in Central Europe may be sufficiently common to consider sensitive newborn screening programs for this disease.
Hum Mutat 2001 Dec
PMID:Cystathionine beta-synthase deficiency in Central Europe: discrepancy between biochemical and molecular genetic screening for homocystinuric alleles. 1174 55

Methylenetetrahydrofolate reductase (MTHFR) deficiency was identified in two out of four children born from nonconsanguineous parents. One of the affected children exhibited some clinical findings suggesting cystathionine beta-synthase deficiency; MTHFR activity was extremely reduced. In addition, hyperhomocysteinaemia, hypomethioninaemia, low total folate, especially methylfolate in red blood cells, and a reduced methylfolate/total folate ratio were found. Two mutations not yet reported, one on exon 1 of the gene changing an arginine to stop codon and one other on exon 9 changing an arginine to tryptophan were identified in both children in the compound heterozygous state associated with a common polymorphism, 1298A>C, also in the heterozygous state. The mother, homozygous for the mutation on exon 9 and for the polymorphism 1298A>C on exon 7, was clinically and biochemically normal, with normal folate status, mainly methylfolate levels in red blood cells, although MTHFR activity was moderately decreased. The father, heterozygous for the transition arginine to stop codon and for the common polymorphism 677C>T on exon 4, exhibited major biochemical abnormalities, hyperhomocysteinaemia and low methylfolate levels in red blood cells, but was clinically normal. The unaffected children had a biochemical pattern close to that of their mother and were heterozygous for the mutation on exon 9 and also for the two common polymorphisms, 677C>T and 1298A>C. In the affected children, some biochemical abnormalities, including folate status, especially methylfolate levels, were improved with treatment combining methyltetrahydrofolic acid, hydroxocobalamin, pyridoxine and betaine; however, homocysteine concentrations remained high and methionine concentrations were lowered. The father was treated with folic acid, which partially improved biochemical abnormalities. The impact of these mutations is discussed.
J Inherit Metab Dis 2001 Dec
PMID:Impact of new mutations in the methylenetetrahydrofolate reductase gene assessed on biochemical phenotypes: a familial study. 1191 16

Hyperhomocysteinemia is an independent risk factor for vascular disease, frequently observed in patients with severe renal impairment. Hyperhomocysteinemia has never been considered as a possible risk factor in renal artery stenosis. We investigated plasma folate and vitamin B12, methylenetetrahydrofolate reductase (MTHFR) C677T and cystathionine beta-synthase (CBS) 844ins68 polymorphisms, and homocysteine levels before and after methionine (100 mg/kg) loading in 58 patients with angiographically documented renal artery stenosis and mildly impaired renal function. One hundred and two normotensive subjects with angiographically normal coronary arteries and no history or clinical or angiographic evidence of atherosclerosis in other vascular districts, were considered as a control group. Mean total homocysteine levels were significantly higher in patients than in controls (P<0.01), as was the prevalence of hyperhomocysteinemia (51.7% vs. 32.3%, P<0.05). However, MTHFR alleles and genotypes as well as CBS 844ins68 mutation frequencies were similar in the two groups, whereas a lower folate level was observed in the patients. Moreover, patients with MTHFR A/A genotype showed a poorer folate status than control subjects, suggesting that a subclinical folate deficiency may be very frequent in renal artery stenosis, regardless of C677T mutation. In conclusions, hyperhomocysteinemia is common in patients with atheromatous renal artery stenosis; a subclinical folate deficiency seems to be involved, regardless of MTHFR thermolabile or CBS insertion genotypes. Folate supplementation might be useful in the management of overall vascular risk of these patients.
Clin Exp Med 2001 Dec
PMID:Homocysteine and atheromatous renal artery stenosis. 1191 80

Cystathionine beta-synthase is a tetrameric hemeprotein that catalyzes the pyridoxal 5'-phosphate-dependent condensation of serine and homocysteine to cystathionine. We have used deletion mutagenesis of both the N and C termini to investigate the functional organization of the catalytic and regulatory regions of this enzyme. Western blot analysis of these mutants expressed in Escherichia coli indicated that residues 497-543 are involved in tetramer formation. Deletion of the 70 N-terminal residues resulted in a heme-free protein retaining 20% of wild type activity. Additional deletion of 151 C-terminal residues from this mutant resulted in an inactive enzyme. Expression of this double-deletion mutant as a glutathione S-transferase fusion protein generated catalytically active protein (15% of wild type activity) that was unaffected by subsequent removal of the fusion partner. The function of the N-terminal region appears to be primarily steric in nature and involved in the correct folding of the enzyme. The C-terminal region of human cystathionine beta-synthase contains two hydrophobic motifs designated "CBS domains." Partial deletion of the most C-terminal of these domains decreased activity and caused enzyme aggregation and instability. Removal of both of these domains resulted in stable constitutively activated enzyme. Deletion of as few as 8 C-terminal residues increased enzyme activity and abolished any further activation by S-adenosylmethionine indicating that the autoinhibitory role of the C-terminal region is not exclusively a function of the CBS domains.
J Biol Chem 2002 Dec 13
PMID:Deletion mutagenesis of human cystathionine beta-synthase. Impact on activity, oligomeric status, and S-adenosylmethionine regulation. 1237 55

Mutations in the gene encoding the gamma(2) subunit of the AMP-activated protein kinase (AMPK) have recently been shown to cause cardiac hypertrophy and ventricular pre-excitation (Wolff-Parkinson-White syndrome). We have examined the effect of four of these mutations on AMPK activity. The mutant gamma(2) polypeptides are all able to form functional complexes following co-expression with either alpha(1)beta(1) or alpha(2)beta(1) in mammalian cells. None of the mutations caused any detectable change in the phosphorylation of threonine 172 within the alpha subunit of AMPK. Consequently, in the absence of an appropriate stimulus the mutant complexes, like the wild-type complex, exist in an inactive form demonstrating that the mutations do not lead to constitutive activation of the kinase. Three of the mutations we studied occur within the cystathionine beta-synthase (CBS) domains of gamma(2). Two of these mutations lead to a marked decrease in AMP dependence, whereas the third reduces AMP sensitivity. These findings suggest that the CBS domains play an important role in AMP-binding within the complex. In contrast, a fourth mutation, which lies between adjacent CBS domains, has no significant effect on AMPK activity in vitro. These results indicate that mutations in gamma(2) have different effects on AMPK function, suggesting that they may lead to abnormal development of the heart through distinct mechanisms.
J Biol Chem 2002 Dec 27
PMID:Functional analysis of mutations in the gamma 2 subunit of AMP-activated protein kinase associated with cardiac hypertrophy and Wolff-Parkinson-White syndrome. 1239 75


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