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)

Cystathionine beta-synthase (CBS) is a unique heme enzyme that catalyzes a PLP-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an autosomal recessively inherited disease of sulfur metabolism. A truncated form of CBS in which the C-terminal amino-acid residues have been deleted has been prepared. The truncated CBS subunits form a dimer, in contrast to the full-length subunits which form tetramers and higher oligomers. The truncated CBS yielded crystals diffracting to 2.6 A which belong to space group P3(1) or P3(2). This is the first comprehensive structural investigation of a PLP and heme-containing enzyme.
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PMID:Crystallization and preliminary X-ray diffraction analysis of the active core of human recombinant cystathionine beta-synthase: an enzyme involved in vascular disease. 1117 83

Homocystinuria is most frequently due to deficiency of cystathionine beta-synthase (CBS). We identified IVS12 as a polymorphism hot spot of the human CBS gene and report five novel single nucleotide polymorphisms (SNPs): g.13514G>A, g.13617A>G, g.13715C>T, g.13800G>A, and g.13904C>T. Analyzing 50 control DNA samples of unaffected and unrelated subjects of German origin the observed frequencies of heterozygosity were 0.02, 0.36, 0.18, 0.36, and 0.36, respectively. These polymorphic markers were combined into four distinct IVS12-haplotypes A1, A2, B1, and B2, revealing frequencies of 0.75, 0.01, 0.15, and 0.09, respectively, with an observed overall frequency of heterozygosity at 0.38. This haplotype system and the SNP c.699 were employed in the analysis of ten alleles affected by the most prevalent CBS mutation, c.833T>C (exon 8; I278T). We found that the I278T alleles segregate with at least two distinct haplotypes characterized by upstream and downstream polymorphic sites instead of sharing a common ancestral haplotype. This was a remarkable finding even in patients with very similar ethnic background. The novel haplotype system may facilitate future studies on the evolution of the CBS gene and might be suited for genotyping of families affected by homocystinuria.
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PMID:Haplotyping of wild type and I278T alleles of the human cystathionine beta-synthase gene based on a cluster of novel SNPs in IVS12. 1129 35

During the past 20 years, cystathionine beta-synthase (CBS) deficiency has been detected in the former Czechoslovakia with a calculated frequency of 1:349,000. The clinical manifestation was typical of homocystinuria, and about half of the 21 patients were not responsive to pyridoxine. Twelve distinct mutations were detected in 30 independent homocystinuric alleles. One half of the alleles carried either the c.833 T-->C or the IVS11-2A-->C mutation; the remaining alleles contained private mutations. The abundance of five mutant mRNAs with premature stop codons was analyzed by PCR-RFLP. Two mRNAs, c.828_931ins104 (IVS7+1G-->A) and c.1226 G-->A, were severely reduced in the cytoplasm as a result of nonsense-mediated decay. In contrast, the other three mRNAs-c.19_20insC, c.28_29delG, and c.210_235del26 (IVS1-1G-->C)-were stable. Native western blot analysis of 14 mutant fibroblast lines showed a paucity of CBS antigen, which was detectable only in aggregates. Five mutations-A114V (c.341C-->T), A155T (c.463G-->A), E176K (c.526G-->A), I278T (c.833T-->C), and W409_G453del (IVS11-2A-->C)-were expressed in Escherichia coli. All five mutant proteins formed substantially more aggregates than did the wild-type CBS, and no aggregates contained heme. These data suggest that abnormal folding, impaired heme binding, and aggregation of mutant CBS polypeptides may be common pathogenic mechanisms in CBS deficiency.
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PMID:Impaired heme binding and aggregation of mutant cystathionine beta-synthase subunits in homocystinuria. 1135 13

Classical homocystinuria due to cystathionine beta-synthase deficiency is one of the disorders revealing a high risk of thromboembolic events and vascular disease. This autosomal-recessively inherited metabolic disorder is considered to be rare with an estimated prevalence of 1:130,000 in the German population. In this study, we developed a novel multiplex PCR generating allele specific fragment lengths to analyse individual genotypes of the two most frequent cystathionine beta-synthase alterations, the I278T mutation, which is worldwide found on up to the half of homocystinuric alleles, and the adjacent polymorphism 844ins68. Screening of 200 unrelated German control subjects revealed a frequency of heterozygosity of 1.5% for 1278T corresponding to a calculated frequency of homozygosity of 1:17.800. Our data indicate that homocystinuria due to cystathionine beta-synthase deficiency is a frequently unrecognized disorder resulting in a high risk of thromboembolic events.
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PMID:High prevalence of the I278T mutation of the human cystathionine beta-synthase detected by a novel screening application. 1143 6

Cystathionine beta-synthase (CBS) is a unique heme- containing enzyme that catalyzes a pyridoxal 5'-phosphate (PLP)-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an inherited disease of sulfur metabolism characterized by increased levels of the toxic metabolite homocysteine. Here we present the X-ray crystal structure of a truncated form of the enzyme. CBS shares the same fold with O-acetylserine sulfhydrylase but it contains an additional N-terminal heme binding site. This heme binding motif together with a spatially adjacent oxidoreductase active site motif could explain the regulation of its enzyme activity by redox changes.
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PMID:Structure of human cystathionine beta-synthase: a unique pyridoxal 5'-phosphate-dependent heme protein. 1148 94

Venous and arterial thromboembolism can occur in patients with homocystinuria. Resistance to activated protein C, which is caused by a single point mutation in the gene for factor V, renders an individual at risk for thrombosis. It has been suggested that coexistence of hereditary homocystinuria and factor V Leiden mutation might jointly play a role in the development of thrombosis. We analysed six patients with homocystinuria due to cystathionine beta-synthase deficiency for factor V Leiden and prothrombin G20210A mutations. Only one patient was found to have the factor V Leiden mutation in homozygous form and this patient had suffered from severe thrombosis. One patient was found to be heterozygous with no documented thrombosis. None of the patients had prothrombin G20210A mutation. We stress the necessity for screening for known thrombophilic risk factors in patients with cystathonine beta-synthase deficiency. The coexistence of the factor V Leiden mutation can cause severe thrombotic events in patients with homocystinuria.
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PMID:Factor V Leiden mutation in Turkish patients with homozygous cystathionine beta-synthase deficiency. 1148 2

Cystathionine beta-synthase (CBS), condensing homocysteine and serine, represents a key regulatory point in the biosynthesis of cysteine via the transsulfuration pathway. Inherited deficiency of CBS causes homocystinuria. CBS is activated by S-adenosyl-L-methionine (AdoMet) by inducing a conformational change involving a noncatalytic C-terminal region spanning residues 414-551. We report the purification of two patient-derived C-terminal mutant forms of CBS, S466L and I435T, that provide new insight into the mechanism of CBS regulation and indicate a regulatory function for the "CBS domain". Both of these point mutations confer catalytically active proteins. The I435T protein is AdoMet inducible but is 10-fold less responsive than wild-type (WT) CBS to physiologically relevant concentrations of this compound. The S466L form does not respond to AdoMet but is constitutively activated to a level intermediate between those of WT CBS in the presence and absence of AdoMet. Both mutant proteins are able to bind AdoMet, indicating that their impairment is related to their ability to assume the fully activated conformation that AdoMet induces in WT CBS. We found that I435T and WT CBS can be activated by partial thermal denaturation but that the AdoMet-stimulated WT, S466L, and a truncated form of CBS lacking the C-terminal region cannot be further activated by this treatment. Tryptophan and PLP fluorescence data for these different forms of CBS indicate that activation by AdoMet, limited proteolysis, and thermal denaturation share a common mechanism involving the displacement of an autoinhibitory domain located in the C-terminal region of the protein.
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PMID:Regulation of human cystathionine beta-synthase by S-adenosyl-L-methionine: evidence for two catalytically active conformations involving an autoinhibitory domain in the C-terminal region. 1152 6

The pathological sequelae of untreated homocystinuria due to cystathionine beta-synthase deficiency include ectopia lentis, osteoporosis, thromboembolic events and mental retardation. They occur at a significantly higher rate with poorer mental capabilities (mean IQ = 57) in the untreated pyridoxine-nonresponsive individuals. The mental capabilities of 23 pyridoxine-nonresponsive individuals with 339 patient-years of treatment were assessed using age-appropriate psychometric tests and were compared to those of 10 unaffected siblings (controls). Of the 23 individuals, 19 were diagnosed through newborn screening with early treatment, two were late-detected and two were untreated at the time of assessment. Thirteen of the newborn, screened group who were compliant with treatment had no complications, while the remaining 6, who had poor compliance, developed complications. Good compliance was defined by a lifetime plasma free homocystine median < 11 micromol/L. The newborn screened, good compliance group (n = 13) with a mean age of 14.4 years (range 4.4-24.9) had mean full-scale IQ (FIQ) of 105.8 (range 84-120), while the poorly compliant group (n = 6) with a mean age of 19.9 years (range 13.8-25.5) had a mean FIQ of 80.8 (range 40-103). The control group (n = 10) with mean age of 19.4 years (range 9.7-32.9) years had a mean FIQ of 102 (range 76-116). The two late-detected patients aged 18.9 and 18.8 years had FIQ of 80 and 102, while the two untreated patients aged 22.4 and 11.7 years had FIQ of 52 and 53, respectively. There was no statistical evidence of significant differences between the compliant, early-treated individuals and their unaffected siblings (controls) except for the FIQ, which was significantly higher than that of the unaffected siblings (p = 0.0397). These data, despite the relatively small numbers, suggest that early treatment with good biochemical control (lifetime plasma free homocystine median < 11 micromol/L) seems to prevent mental retardation.
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PMID:The intellectual abilities of early-treated individuals with pyridoxine-nonresponsive homocystinuria due to cystathionine beta-synthase deficiency. 1159 48

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.
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PMID:Vascular outcome in patients with homocystinuria due to cystathionine beta-synthase deficiency treated chronically: a multicenter observational study. 1174 88

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.
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PMID:Cystathionine beta-synthase deficiency in Central Europe: discrepancy between biochemical and molecular genetic screening for homocystinuric alleles. 1174 55


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