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

Little is known about the genes and enzymes involved in sulfur assimilation in Bacillus subtilis, or about the regulation of their expression or activity. To identify genes regulated by sulfur limitation, the authors used two- dimensional (2D) gel electrophoresis to compare the proteome of a wild-type strain grown with either sulfate or glutathione as sole sulfur source. A total of 15 proteins whose synthesis is modified under these two conditions were identified by matrix-assisted laser desorption/ionization time of flight (MALDI TOF) mass spectrometry. In the presence of sulfate, an increased amount of proteins involved in the metabolism of C(1) units (SerA, GlyA, FolD) and in the biosynthesis of purines (PurQ, Xpt) and pyrimidines (Upp, PyrAA, PyrF) was observed. In the presence of glutathione, the synthesis of two uptake systems (DppE, SsuA), an oxygenase (SsuD), cysteine synthase (CysK) and two proteins of unknown function (YtmI, YurL) was increased. The changes in expression of the corresponding genes, in the presence of sulfate and glutathione, were monitored using slot-blot analyses and lacZ fusions. The ytmI gene is part of a locus of 12 genes which are co-regulated in response to sulfur availability. This putative operon is activated by a LysR-like regulator, YTLI: This is the first regulator involved in the control of expression in response to sulfur availability to be identified in B. subtilis.
 ...
PMID:Sulfur-limitation-regulated proteins in Bacillus subtilis: a two-dimensional gel electrophoresis study. 1139 Jun 94

Elevated levels of homocysteine, a sulfur-containing amino acid, are correlated with increased risk for cardiovascular diseases and Alzheimers disease and with neural tube defects. The only route for the catabolic removal of homocysteine in mammals begins with the pyridoxal phosphate- (PLP-) dependent beta-replacement reaction catalyzed by cystathionine beta-synthase. The enzyme has a b-type heme with unusual spectroscopic properties but as yet unknown function. The human enzyme has a modular organization and can be cleaved into an N-terminal catalytic core, which retains both the heme and PLP-binding sites and is highly active, and a C-terminal regulatory domain, where the allosteric activator S-adenosylmethionine is presumed to bind. Studies with the isolated recombinant enzyme and in transformed human liver cells indicate that the enzyme is approximately 2-fold more active under oxidizing conditions. In addition to heme, the enzyme contains a CXXC oxidoreductase motif that could, in principle, be involved in redox sensing. In this study, we have examined the role of heme versus the vicinal thiols in modulating the redox responsiveness of the enzyme. Deletion of the heme domain leads to loss of redox sensitivity. In contrast, substitution of either cysteine with a non-redox-active amino acid does not affect the responsiveness of the enzyme to reductants. We also report the crystal structure of the catalytic core of the enzyme in which the vicinal cysteines are reduced without any discernible differences in the remainder of the protein. The structure of the catalytic core is compared to those of other members of the fold II family of PLP-dependent enzymes and provides insights into active site residues that may be important in interacting with the substrates and intermediates.
 ...
PMID:Human cystathionine beta-synthase is a heme sensor protein. Evidence that the redox sensor is heme and not the vicinal cysteines in the CXXC motif seen in the crystal structure of the truncated enzyme. 1217 32

Despite the availability of genome data and recent advances in methionine regulation in Corynebacterium glutamicum, sulfur metabolism and its underlying molecular mechanisms are still poorly characterized in this organism. Here, we describe the identification of an ORF coding for a putative regulatory protein that controls the expression of genes involved in sulfur reduction dependent on extracellular methionine levels. C. glutamicum was randomly mutagenized by transposon mutagenesis and 7,000 mutants were screened for rapid growth on agar plates containing the methionine antimetabolite D,L-ethionine. In all obtained mutants, the site of insertion was located in the ORF NCgl2640 of unknown function that has several homologues in other bacteria. All mutants exhibited similar ethionine resistance and this phenotype could be transferred to another strain by the defined deletion of the NCgl2640 gene. Moreover, inactivation of NCgl2640 resulted in significantly increased methionine production. Using promoter lacZ-fusions of genes involved in sulfur metabolism, we demonstrated the relief of L-methionine repression in the NCgl2640 mutant for cysteine synthase, o-acetylhomoserine sulfhydrolase (metY) and sulfite reductase. Complementation of the mutant strain with plasmid-borne NCgl2640 restored the wild-type phenotype for metY and sulfite reductase.
 ...
PMID:Single-gene knockout of a novel regulatory element confers ethionine resistance and elevates methionine production in Corynebacterium glutamicum. 1566 56

Sinorhizobium fredii USDA257, a soybean symbiont, exports several nodulation outer proteins (Nops) into the rhizosphere. These proteins, which are exported by a type III secretion system (TTSS), have a pivotal role in host-specific nodulation. The entire TTSS of S. fredii lies within a 31-kb region that includes conserved genes that code for secretion machinery proteins, Nops, and several open reading frames (ORF) of unknown function. Identifying the functions of these ORF is essential to understand fully the role of TTSS in nodulation. Here, we report the characterization of y4xP, an ORF of previously unknown function. Southern blot analysis revealed that USDA257 contains two copies of y4xP, while a sibling, USDA191, contains a single copy. The amino acid sequence of Y4XP is homologous to both eukaryotic and prokaryotic cysteine synthase, a key enzyme in sulfur assimilation. The coding region of USDA257 y4xP under control of T7 promoter was expressed in Escherichia coli, and the recombinant protein was purified by nickel-affinity chromatography. Antibodies generated against soybean cysteine synthase cross-reacted with the recombinant protein. A nonpolar mutant of y4xP of USDA191 showed a marked reduction in cysteine synthase activity. Enzyme activity was completely restored when the mutant was complemented with a plasmid containing the y4xP sequence. Cysteine synthase activity was confined to the cell cytosol. Extracellular protein fraction from genistein-induced USDA191 showed no cysteine synthase activity. This observation indicates that cysteine synthase, which is located in the TTSS locus, is not a type III secreted protein. A nonpolar cysteine synthase mutant was able to export all the Nops to the rhizosphere, albeit in reduced amounts compared with the wild-type USDA191. Interestingly, USDA191 cysteine synthase mutant was able to initiate nodules on 'McCall' soybean more efficiently than the wild-type. Our results demonstrate that y4xP encodes a cysteine synthase and inactivation of this gene enhances the ability of USDA191 to form nodules on 'McCall' soybean by regulating Nops production.
 ...
PMID:Y4xP, an open reading frame located in a type III protein secretion system locus of Sinorhizobium fredii USDA257 and USDA191, encodes cysteine synthase. 1677 97

Cystathionine beta-synthase (CBS) is a homocysteine metabolizing enzyme that contains pyridoxal phosphate (PLP) and a six-coordinate heme cofactor of unknown function. CBS was inactivated by peroxynitrite, the product of nitric oxide and superoxide radicals. The IC(50) was approximately 150microM for 5microM ferric CBS. Stopped-flow kinetics and competition experiments showed a direct reaction with a second-order rate constant of (2.4-5.0)x10(4)M(-1)s(-1) (pH 7.4, 37 degrees C). The radicals derived from peroxynitrite, nitrogen dioxide and carbonate radical, also inactivated CBS. Exposure to peroxynitrite did not modify bound PLP but led to nitration of Trp208, Trp43 and Tyr223 and alterations in the heme environment including loss of thiolate coordination, conversion to high-spin and bleaching, with no detectable formation of oxo-ferryl compounds nor promotion of one-electron processes. This study demonstrates the susceptibility of CBS to reactive oxygen/nitrogen species, with potential relevance to hyperhomocysteinemia, a risk factor for cardiovascular diseases.
 ...
PMID:Inactivation of cystathionine beta-synthase with peroxynitrite. 1973 48

Cystathionine beta-synthase (CBS) domains are small motifs that are present in proteins with completely different functions. Several genetic diseases in humans have been associated with mutations in their sequence, which has made them promising targets for rational drug design. The protein MJ0100 from Methanocaldococcus jannaschii includes a DUF39 domain of so far unknown function and a CBS domain pair (Bateman domain) at its C-terminus. This work presents the crystallographic analysis of four different states of the CBS motif pair of MJ0100 in complex with different numbers of S-adenosyl-L-methionine (SAM) and S-methyl-5'-thioadenosine (MTA) ligands, providing evidence that ligand-induced conformational reorganization of Bateman domain dimers could be an important regulatory mechanism. These observations are in contrast to what is known from most of the other Bateman domain structures but are supported by recent studies on the magnesium transporter MgtE. Our structures represent the first example of a CBS domain protein complexed with SAM and/or MTA and might provide a structural basis for understanding the molecular mechanisms regulated by SAM upon binding to the C-terminal domain of human CBS, whose structure remains unknown.
 ...
PMID:Binding of S-methyl-5'-thioadenosine and S-adenosyl-L-methionine to protein MJ0100 triggers an open-to-closed conformational change in its CBS motif pair. 2002 78