Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.5.1.47 (cysteine synthase)
625 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Four cDNA clones, rcs1, rcs2, rcs3 and rcs4, encoding cysteine synthase [O-acetylserine(thiol)lyase] were isolated from rice. The predicted amino acid sequences contain the conserved PXXSVKDR region characteristic of cysteine synthase, which includes the lysine residue that binds the cofactor, pyridoxal 5'-phosphate. Molecular phylogenic analysis suggests that, whereas rcs1 and rcs3 belong to the cytosolic isoform family, rcs2 and rcs4 form a new family of cysteine synthase. Transcript accumulation of each gene was examined for organ specificity, and also for response to sulfur, nitrogen and light. The rcs1 transcript accumulated in all organs examined, and was induced in shoots and roots upon sulfur starvation under non-limiting nitrogen conditions. The rcs2 transcript accumulated in shoots grown in the light, but disappeared almost completely by dark treatment. The rcs3 transcript was found more abundantly in roots than in shoots, and was reduced in the dark, as well as under sulfur and nitrogen deprivation. The rcs4 transcript was scarce in all organs examined. These observations indicate that cysteine synthase genes encode functionally distinct cysteine synthase isoforms, and that they are coordinately regulated by the availability of sulfur, nitrogen, and light.
...
PMID:Four rice genes encoding cysteine synthase: isolation and differential responses to sulfur, nitrogen and light. 1009 15

Covalent binding of L-methionine as an external aldimine to the pyridoxal 5'-phosphate-cofactor in the K41A mutant of O-acetylserine sulfhydrylase from Salmonella typhimurium induces a large conformational change in the protein. Methionine mimics the action of the substrate O-acetyl-L-serine during catalysis. The alpha-carboxylate moiety of L-methionine in external aldimine linkage with the active site pyridoxal 5'-phosphate forms a hydrogen bonding network to the "asparagine-loop" P67-T68-N69-G70 which adopts a different conformation than in the native protein. The side-chain nitrogen of Asn69 moves more than 7 A to make a hydrogen bond to the alpha-carboxylate group of the inhibitor. As the external aldimine is formed, the PLP tilts by 13 degrees along its longitudinal axis such that C4' moves toward the entrance to the active site and the side-chain of the methionine is directed toward the active site entrance. The local rearrangement acts as a trigger to induce a large global conformational change in the protein. A subdomain comprised of beta-strand 4, alpha-helix 3, beta-strand 5 and alpha-helix 4 moves towards the active site by a rotation of 7 degrees. This subdomain movement results in a reduction of the severe twist of its central beta-sheet and reduces the active site entrance to a small hole, giving access only to small molecules like sulfide, the second substrate, or acetate, the first product.
...
PMID:Ligand binding induces a large conformational change in O-acetylserine sulfhydrylase from Salmonella typhimurium. 1045 98

Cysteine is the major source of fixed sulfur for the synthesis of sulfur-containing compounds in organisms of the Bacteria and Eucarya domains. Though pathways for cysteine biosynthesis have been established for both of these domains, it is unknown how the Archaea fix sulfur or synthesize cysteine. None of the four archaeal genomes sequenced to date contain open reading frames with identities to either O-acetyl-L-serine sulfhydrylase (OASS) or homocysteine synthase, the only sulfur-fixing enzymes known in nature. We report the purification and characterization of OASS from acetate-grown Methanosarcina thermophila, a moderately thermophilic methanoarchaeon. The purified OASS contained pyridoxal 5'-phosphate and catalyzed the formation of L-cysteine and acetate from O-acetyl-L-serine and sulfide. The N-terminal amino acid sequence has high sequence similarity with other known OASS enzymes from the Eucarya and Bacteria domains. The purified OASS had a specific activity of 129 micromol of cysteine/min/mg, with a K(m) of 500 +/- 80 microM for sulfide, and exhibited positive cooperativity and substrate inhibition with O-acetyl-L-serine. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single band at 36 kDa, and native gel filtration chromatography indicated a molecular mass of 93 kDa, suggesting that the purified OASS is either a homodimer or a homotrimer. The optimum temperature for activity was between 40 and 60 degrees C, consistent with the optimum growth temperature for M. thermophila. The results of this study provide the first evidence for a sulfur-fixing enzyme in the Archaea domain. The results also provide the first biochemical evidence for an enzyme with the potential for involvement in cysteine biosynthesis in the Archaea.
...
PMID:O-Acetylserine sulfhydrylase from Methanosarcina thermophila. 1061 61

Proteins belonging to the superfamily of pyridoxal 5'-phosphate-dependent enzymes are currently classified into three functional groups and five distinct structural fold types. The variation within this enzyme group creates an ideal system to investigate the relationships among amino acid sequences, folding pathways, and enzymatic functions. The number of known three-dimensional structures of pyridoxal 5'-phosphate-dependent enzymes is rapidly increasing, but only for relatively few have the folding mechanisms been characterized in detail. The dimeric O-acetylserine sulfhydrylase from Salmonella typhimurium belongs to the beta-family and fold type II group. Here we report the guanidine hydrochloride-induced unfolding of the apo- and holoprotein, investigated using a variety of spectroscopic techniques. Data from absorption, fluorescence, circular dichroism, (31)P nuclear magnetic resonance, time-resolved fluorescence anisotropy, and photon correlation spectroscopy indicate that the O-acetylserine sulfhydrylase undergoes extensive disruption of native secondary and tertiary structure before monomerization. Also, we have observed that the holo-O-acetylserine sulfhydrylase exhibits a greater conformational stability than the apoenzyme form. The data are discussed in light of the fact that the role of the coenzyme in structural stabilization varies among the pyridoxal 5'-phosphate-dependent enzymes and does not seem to be linked to the particular enzyme fold type.
...
PMID:Role of pyridoxal 5'-phosphate in the structural stabilization of O-acetylserine sulfhydrylase. 1099 67

O-acetylserine sulfhydrylase, a homo-dimeric enzyme from Salmonella typhimurium, covalently binds one pyridoxal 5'-phosphate molecule per subunit as a fluorescent coenzyme. Different tautomers of the Schiff base between the coenzyme and lysine 41 generate structured absorption and fluorescence spectra upon one-photon excitation. We investigated the protein population heterogeneity by fluorescence correlation spectroscopy and lifetime techniques upon two-photon excitation. We sampled the fluorescence intensity from a small number of molecules (approximately 10) and analyzed the distribution of photon counts to separately determine the number and the fluorescence brightness of excited protein molecules. The changes in the average number of molecules and in the fluorescence brightness with the excitation wavelength indicate the presence of at least two fluorescent species, with two-photon excitation maxima at 660 and 800 nm. These species have been identified as the enolimine and ketoenamine tautomers of the protein-coenzyme internal aldimine. Their relative abundance is estimated to be 4:1, whereas the ratio of their two-photon cross sections is reversed with respect to the single-photon excitation case. Consistent results are obtained from the measurement of the lifetime decays, which are sensitive to the excited-state heterogeneity. At least two components were detected, with lifetimes of approximately 2.5 and 0.5 ns. The lifetimes are very close to the values measured in bulk solutions upon one-photon excitation and attributed to the ketoenamine tautomer and to a dipolar species formed upon proton dissociation in the excited state.
...
PMID:Molecular heterogeneity of O-acetylserine sulfhydrylase by two-photon excited fluorescence fluctuation spectroscopy. 1125 10

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.
...
PMID:Structure of human cystathionine beta-synthase: a unique pyridoxal 5'-phosphate-dependent heme protein. 1148 94

Proteins utilizing pyridoxal 5'-phosphate as a coenzyme constitute a large superfamily and are currently classified into three functional groups and five structural fold types. Despite the variability of sequences and catalyzed reactions, they share relevant structural, dynamic and functional properties. Therefore, they constitute an optimal system to investigate the relative influence of primary sequence and coenzyme interactions on folding pathways, structural stability and enzymatic function. O-Acetylserine sulfhydrylase is a dimeric pyridoxal 5'-phosphate dependent enzyme that catalyzes the synthesis of L-cysteine from O-acetylserine and sulfide. The time-resolved fluorescence study of O-acetylserine sulfhydrylase unfolding, here reported, indicates that the coenzyme stabilizes the protein structure. The dependence on denaturant concentration of tryptophan lifetimes in the holo- and apo-enzyme demonstrates that the interactions with the coenzyme stabilize the C-terminal domain to a higher extent with respect to the N-terminal domain. This result is discussed in terms of a linkage between the differential stabilization brought about by the coenzyme and the different degrees of conformational flexibility required by the specialized functional role of distinct protein regions.
...
PMID:Unfolding of pyridoxal 5'-phosphate-dependent O-acetylserine sulfhydrylase probed by time-resolved tryptophan fluorescence. 1198 20

An O-acetylserine sulfhydrylase (OASS) from the hyperthermophilic archaeon Aeropyrum pernix K1, which shares the pyridoxal 5'-phosphate binding motif with both OASS and cystathionine beta-synthase (CBS), was cloned and expressed by using Escherichia coli Rosetta(DE3). The purified protein was a dimer and contained pyridoxal 5'-phosphate. It was shown to be an enzyme with CBS activity as well as OASS activity in vitro. The enzyme retained 90% of its activity after a 6-h incubation at 100 degrees C. In the O-acetyl-L-serine sulfhydrylation reaction, it had a pH optimum of 6.7, apparent K(m) values for O-acetyl-L-serine and sulfide of 28 and below 0.2 mM, respectively, and a rate constant of 202 s(-1). In the L-cystathionine synthetic reaction, it showed a broad pH optimum in the range of 8.1 to 8.8, apparent K(m) values for L-serine and L-homocysteine of 8 and 0.51 mM, respectively, and a rate constant of 0.7 s(-1). A. pernix OASS has a high activity in the L-cysteine desulfurization reaction, which produces sulfide and S-(2,3-hydroxy-4-thiobutyl)-L-cysteine from L-cysteine and dithiothreitol.
...
PMID:Characterization of a novel thermostable O-acetylserine sulfhydrylase from Aeropyrum pernix K1. 1264 99

O-Acetylserine sulfhydrylase is a homodimeric enzyme catalyzing the last step of cysteine biosynthesis via a Bi Bi ping-pong mechanism. The subunit is composed of two domains, each containing one tryptophan residue, Trp50 in the N-terminal domain and Trp161 in the C-terminal domain. Only Trp161 is highly conserved in eucaryotes and bacteria. The coenzyme pyridoxal 5'-phosphate is bound in a cleft between the two domains. The enzyme undergoes an open to closed conformational transition upon substrate binding. The effect of single Trp to Tyr mutations on O-acetylserine sulfhydrylase structure, function, and stability was investigated with a variety of spectroscopic techniques. The mutations do not significantly alter the enzyme secondary structure but affect the catalysis, with a predominant influence on the second half reaction. The W50Y mutation strongly affects the unfolding pathway due to the destabilization of the intersubunit interface. The W161Y mutation, occurring in the C-terminal domain, produces a reduction of the accessibility of the active site to acrylamide and stabilizes thermodynamically the N-terminal domain, a result consistent with stronger interdomain interactions.
...
PMID:Surface-exposed tryptophan residues are essential for O-acetylserine sulfhydrylase structure, function, and stability. 1281 39

In this study, the phosphoproteome of Corynebacterium glutamicum, an industrially important soil bacterium of the Corynebacterium/Mycobacterium/Nocardia (CMN) group of Gram-positive bacteria, was investigated by two different detection methods: first, by in vivo radio-labeling using [(33)P]-phosphoric acid with subsequent autoradiography and second, by immunostaining with phosphoamino acid-specific monoclonal antibodies. After two-dimensional gel electrophoresis (2-DE), around 60 [(33)P]-labeled protein spots were visualized and around 90 antibody-decorated protein spots detected; 31 of the protein spots were detected with both methods. By peptide mass fingerprinting, 41 different proteins were identified, namely 5-enolpyruvylshikimate 3-phosphate synthase, aconitase, acyl-CoA carboxylase, acyl-CoA synthetase, ATP (synthase alpha- and beta-chain), carbamoyl-phosphate synthase, citrate synthase, cysteine synthase, DnaK, the elongation factors G, P, Ts and Tu, enolase, fructose bisphosphate aldolase, fumarase, Gap dehydrogenase, glutamine synthetase I, glycine hydroxymethyltransferase, GroEL2, GTPase, heat-inducible transcriptional repressor DnaJ2, inorganic pyrophosphatase, isocitrate dehydrogenase, ketol-acid reductoisomerase, lactate dehydrogenase, leucine-tRNA ligase, lipoamide dehydrogenase, methionine synthase, O-acetylhomoserine sulfhydrylase, pyruvate carboxylase, pyruvate kinase, pyruvate oxidase, ribosomal protein S1, RNA polymerase (beta-subunit), succinyl-CoA:CoA transferase, transketolase and UDP-N-acetylmuramoyl-L-alanine ligase, besides a hypothetical 35k protein and a hypothetical glucose kinase. Both detection techniques were used to create a phosphoproteome map. Additionally, the influence of nitrogen deprivation on the phosphoproteome of C. glutamicum was investigated.
...
PMID:Towards a phosphoproteome map of Corynebacterium glutamicum. 1292 88


<< Previous 1 2 3 4 5 6 Next >>

---