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At least 19 recordsLinked to original sources
PubMed1988

Synthesis of beauvericin by a multifunctional enzyme.

Beauvericin synthetase, a multifunctional enzyme catalyzing depsipeptide formation in Beauveria bassiana was purified to near homogeneity. The enzyme consists of a single polypeptide chain with a molecular mass of about 250 kdaltons. The mechanism of beauvericin formation is very similar to that of the cyclohexadepsipeptide enniatin. The constituents of the beauvericin molecule, L-phenylalanine and D-alpha-hydroxyisovaleric acid are activated as thioesters via the corresponding adenylates. N-Methylation takes place at the thioester bound stage of the phenylalanine residues. Omission of the methyl donor S-adenosyl-L-methionine results in the formation of demethylbeauvericin. Studies on substrate specificity revealed that phenylalanine could be replaced by a number of other aromatic or aliphatic amino acids like beta-phenylserine, ortho-, meta-, para-fluorophenylalanine, isoleucine, norleucine and leucine. Valine, the constituent amino acid of enniatin B was not accepted by the enzyme.

Anti-Bacterial Agents↗
PubMed1977

Methylenetetrahydrofolate dehydrogenase, methenyltetrahydrofolate cyclohydrolase and formyltetrahydrofolate synthetase from porcine liver. Isolation of a dehydrogenase-cyclohydrolase fragment from the multifunctional enzyme.

Tryptic digestion of a multifunctional enzyme from porcine liver containing methylenetetrahydrofolate dehydrogenase (5,10-methylenetetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.5), methenyltetrahydrofolate cyclohydrolase (5,10-methenyltetrahydrofolate 5-hydrolase, EC 3.5.4.9) and formyltetrahydrofolate synthetase (formate:tetrahydrofolate ligase, EC 6.3.4.3) activities destroys the synthetase. A fragment containing both dehydrogenase and cyclohydrolase activities has been isolated by affinity chromatography on an NADP+-Sepharose affinity column. The purified fragment is homogeneous on dodecyl sulfate-polyacrylamide gel electrophoresis where its molecular weight was determined as 33 000 +/- 1200 compared with 100 000 for the undigested protein. The cyclohydrolase activity retains sensitivity to inhibition by NADP+, MgATP and ATP.

Aminohydrolases↗
PubMed1992

Molecular cloning and sequencing of the gene for mycocerosic acid synthase, a novel fatty acid elongating multifunctional enzyme, from Mycobacterium tuberculosis var. bovis Bacillus Calmette-Guerin.

Mycocerosyl lipids are found uniquely in the cell walls of pathogenic mycobacteria. Mycocerosic acid synthase (MAS) is a multifunctional protein which catalyzes elongation of n-fatty acyl-CoA with methylamalonyl-CoA as the elongating agent (Rainwater, D. L., and Kolattukudy, P. E. (1985) J. Biol. Chem. 260, 616-623). To understand how the various domains that catalyze the reactions involved in chain elongation are organized, mas gene from Mycobacterium tuberculosis bovis BCG was cloned. A lambda gt11 library of AluI partially digested genomic DNA from the organism was screened with an oligonucleotide probe designed from the N-terminal amino acid sequence of purified MAS. Using terminal segments of inserts from positive clones as the probe, the library was rescreened and the process was repeated. Sequencing of four overlapping clones revealed a contiguous sequence of 9699 base pair(s) (bp) of mycobacterial genome containing a 6330-bp open reading frame that could code for a protein of 2100 amino acids with a molecular mass of 225,437 daltons. The authenticity of the open reading frame as that of MAS was verified by correspondence of the amino acid sequences deduced from the gene with the directly determined amino acid sequences of the N terminus and three different internal peptide fragments. By comparing the MAS amino acid sequence with the sequences in the active site regions of known fatty acid synthases and polyketide synthases the functional domains in MAS were identified. This analysis showed that the domains were organized in the following order: beta-ketoacyl synthase, acyl transferase, dehydratase-enoyl reductase, beta-ketoreductase, acyl carrier protein; no thioesterase-like domain could be found. These results establish MAS as the first case of an elongating multifunctional enzyme composed of two identical subunits that resemble the vertebrate fatty acid synthase in size, subunit structure, and linear organization of functional domains. Southern and Western blot analyses showed absence of mas gene and encoded proteins in Mycobacterium smegmatis and Escherichia coli. This result is consistent with the report that mycocerosic acid is present only in pathogenic mycobacteria.

Acyltransferases↗
PubMed1976

Multifunctional enzyme, bisphosphoglyceromutase/2,3-bisphosphoglycerate phosphatase/phosphoglyceromutase, from human erythrocytes. Evidence for a common active site.

Bisphosphoglyceromutase and 2,3-bisphosphoglycerate phosphatase activities responsible for 2,3-bisphosphoglycerate metabolsim in human red cells are displayed by the same enzyme protein which has phosphoglyceromutase activity [Sasaki, R., et al. (1975) Eur J. Biochem. 50, 581-593]. This enzyme was subjected to chemical modification by trinitrobenzenesulfonate. The three enzyme activities were inactivated by trinitrobenzenesulfonate at the same rate. The sulfhydryl content of the enzyme was unchanged during trinitrophenylation, indicating that derivatization was through the amino group. Trinitrophenylation of about one amino group per mole of the enzyme resulted in complete loss of the three activities. Both 2,3-bisphosphoglycerate and 1,3-bisphosphoglycerate inhibited trinitrophenylation and effectively protected the enzyme from inactivation. Although monophosphoglycerates did not show any protective effect at concentrations which should be adequate based upon their kinetic constants, they were protective at higher concentrations. Inactivation by trinitrophenylation was an apparent first-order reaction. The dissociation constant of the enzyme - 2,3-bisphosphoglycerate complex was determined by analyzing the first-order reaction on the assumption that the protective effect of 2,3-bisphosphoglycerate was due to competition with trinitrobenzenesulfonate. The dissociation constant was in good agreement with kinetic constants of 2,3-bisphosphoglycerate in the enzyme reactions, which indicated that 2,3-bisphosphoglycerate did indeed exert its protective effect through competition with trinitrobenzenesulfonate for an amino group of the enzyme. The protective effect of monophosphoglycerates could be rationalized with kinetic evidence that 2-phosphoglycerate at high concentrations interacts with the 2,3-bisphosphoglycerate binding site. These results indicate that the enzyme exhibits the three enzyme activities at a common active site at which one amino group essential for binding of bisphosphoglycerates is located. Based on the multifunctional properties of this enzyme, a possible mechanism was discussed for regulation of 2,3-bisphosphoglycerate metabolism in human red cells.

Binding Sites↗
PubMed1989

Molecular characterization of a Dictyostelium discoideum gene encoding a multifunctional enzyme of the pyrimidine pathway.

We have isolated and characterized a Dictyostelium discoideum gene (PYR1-3) encoding a multifunctional protein that carries the three first enzymatic activities of the de novo pyrimidine biosynthetic pathway. The PYR1-3 gene is adjacent to another gene of the pyrimidine biosynthetic pathway (PYR4); the two genes are separated by a 1.5-kb non-coding sequence and transcribed divergently. The PYR1-3 gene is transcribed to form a 7.5-kb polyadenylated mRNA. As with the other genes of the pyrimidine biosynthetic pathway, the PYR1-3 mRNA level is high during growth and decreases sharply during development. We have determined the nucleotide sequence of 63% of the coding region of the PYR1-3 gene. We have identified the activities of the protein encoded by the D. discoideum PYR1-3 gene by comparison of amino acid sequences with the products of genes of known function. The PYR1-3 gene contains four distinct regions that probably correspond to four domains in the protein. From the NH2 extremity to the COOH extremity, these domains are: glutamine amidotransferase, carbamoylphosphate synthetase, dihydroorotase and aspartate transcarbamylase. This organization is identical to the one found in the rudimentary gene of Drosophila. The evolutionary implications of this finding are discussed.

Amino Acid Sequence↗
PubMed1992

Enzymatic characterisation of the multifunctional enzyme delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase from Streptomyces clavuligerus.

delta-(L-alpha-Aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase, the multienzyme catalyzing the formation of ACV from the constituent amino acids and ATP in the presence of Mg2+ and dithioerythritol, was purified about 2700-fold from Streptomyces clavuligerus. The molecular mass of the native enzyme as determined by gel filtration chromatography is 560 kDa, while that determined by denaturing gel electrophoresis is 500 kDa. The enzyme is able to catalyze pyrophosphate exchange in dependence on L-cysteine and L-valine, but no L-alpha-aminoadipic-acid-dependent ATP/PPi exchange could be detected. Other L-cysteine- and L-valine-activating enzymes present in crude extracts were identified as aminoacyl-tRNA synthetases which could be separated from ACV synthetase. The molecular mass of these enzymes is 140 kDa for L-valine ligase and 50 kDa for L-cysteine ligase. The dissociation constants have been estimated, assuming three independent activation sites, to be 1.25 mM and 1.5 mM for cysteine and ATP, and 2.4 mM and 0.25 mM for valine and ATP, respectively. The enzyme forms a thioester with alpha-aminoadipic acid and with valine in a molar ratio of 0.6:1 (amino acid/enzyme). Thus, the bacterial ACV synthetase is a multifunctional peptide synthetase, differing from fungal ACV synthetases in its mechanism of activation of the non-protein amino acid.

Amino Acyl-tRNA Synthetases↗
PubMed1989

Pyrimidine biosynthesis in Saccharomyces cerevisiae: the ura2 cluster gene, its multifunctional enzyme product, and other structural or regulatory genes involved in de novo UMP synthesis.

There are six enzymatic steps in the de novo biosynthesis of uridine monophosphate (UMP). In yeast, six structural genes (ura2, ura4, ura1, ura5, ura10, and ura3) and one regulatory gene (PPR1) are involved in this metabolic pathway. Gene ura2 codes for a multifunctional protein that carries the first two enzymatic activities of the pathway, i.e., carbamylphosphate synthetase (CPSase) and aspartate transcarbamylase (ATCase). Gene ura2 has been cloned and sequenced, revealing the presence of three open reading frames, one of which codes for the multifunctional protein, a polypeptide of 2212 amino acids, with a mRNA of 7 +/- 0.3 kilobases. Expression of gene ura2 is regulated at the transcriptional level. As I indicate here, it could also be controlled at the posttranscriptional level since all the consensus sequences for a 1.2-kilobases intron are present in the coding sequence of the open reading frame. The deducted amino acid sequence has allowed the identification of four domains. Starting from the amino terminus of the protein, these are glutamine amido transferase, CPSase, a domain that resembles dihydroorotase (DHOase-like) but does not have DHOase activity, and ATCase. There are also two sites of interest that match known concensus phosphorylation sites; one is located in the distal part of the CPSase domain, the other in the connector region between DHOase-like and ATCase domains. The protein has been purified as a multienzyme aggregate and as a multifunctional protein. The latter form, when isolated from a protease B deficient strain of Saccharomyces cerevisiae, contained mostly polypeptide chains of 220 kilodaltons. Work is currently in progress to determine the site(s) of phosphorylation of this protein in vitro. ATCase activity of both wild-type and protease-deficient strains has been found to be localized in the nucleus. Channeling of carbamyl phosphate, the first intermediate in the pathway, has been demonstrated both in vitro and in permeabilized cells. The other genes of UMP biosynthesis, except for ura5, are regulated by induction of their transcription by the combined action of the product of the ppr1 gene and the inducer, dihydroorotate. Dihydroorotate dehydrogenase activity was found in the cytoplasm. Two isoenzymes of orotate phosphoribosyl transferase have been found, coded for by ura5 and ura10. The products of genes ura10 and ura3 are proposed to participate in the channeling of orotidine monophosphate. The discussion considers the problem posed by the isolation of both multienzyme complexes and multifunctional proteins resulting from the expression of the same cluster genes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Thermodynamics of the reactions catalyzed by the multifunctional enzyme complex tryptophan synthase.

The intrinsic enthalpy changes (corrected for hydration of D-glyceraldehyde 3-phosphate) for the reactions catalyzed by the alpha and beta 2 subunits of tryptophan synthase from Escherichia coli have been determined calorimetrically. Cleavage of indoleglycerol phosphate (alpha reaction) was found to be associated with a delta H value of 54.0 +/- 2.5 kJ mol-1, while condensation of indole with L-serine (beta reaction) involved -80.3 +/- 4.6 kJ mol-1'. By direct determination of the enthalpy concomitant with the overall synthesis of tryptophan from indoleglycerol phosphate and L-serine an enthalpy value of -13.4 +/- 5.6 kJ mol-1 was observed. In view of the uncertainties of the literature data used for calculation of the hydration contribution, the agreement between the directly measured delta H value of the overall reaction and the sum of the enthalpies of the alpha and beta reactions is fair. Deamination of L-serine, a side reaction catalyzed preferentially by the isolated beta 2 pyridoxal 5'-phosphate2 subunit, was shown to be associated with an enthalpy change of -7.3 +/- 0.4 kJ mol-1.

Buffers↗
PubMed1978

Methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase-formyltetrahydrofolate synthetase from porcine liver. Interaction between the dehydrogenase and cyclohydrolase activities of the multifunctional enzyme.

Methylenetetrahydrofolate dehydrogenase (5,10-methylenetetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.5) one of the activities of a trifunctional folate-dependent enzyme from porcine liver, uses an ordered kinetic mechannism as determined from initial velocity, product inhibition and dead-end inhibition studies. The final product released from the dehydrogenase is methenyltetrahydrofolate. However, from the time course of appearance of products it is observed that the methenyltetrahydrofolate, rather than equilibrating with the solution, is converted preferentially to formyltetrahydrofolate by the cyclohydrolase, (5,10-methenyletrahydrofolate 5-hydrolase (decyclizing), EC 3.5.4.9) demonstrating a functional interaction between these two enzymic activites.

Aminohydrolases↗
PubMed1991

6-Hydroxymellein synthetase as a multifunctional enzyme complex in elicitor-treated carrot root extract.

Synthetic activity of a polyketide compound 6-hydroxymellein was induced in elicitor-treated carrot root tissues. The activity was significantly inhibited by an antiserum raised against the acyl carrier protein (ACP) of fatty acid synthetase, suggesting that the enzyme(s) for 6-hydroxymellein synthesis require(s) a functional unit similar to ACP. However, the synthetic activity was not stimulated by the addition of ACP purified from Escherichia coli and was not lost even after fractionation by gel-filtration chromatography. The active fraction obtained by gel-filtration (136 kDa) was subjected to immunoblot analysis, and a 128 kDa polypeptide in the fraction was found to cross-react with anti-ACP serum. These observations suggest that the biosynthesis of 6-hydroxymellein in carrot cells is catalyzed by an enzyme consisting of a single peptide chain.

Acyl Carrier Protein↗
PubMed1987

A eukaryotic repressor protein, the qa-1S gene product of Neurospora crassa, is homologous to part of the arom multifunctional enzyme.

Little is known about the proteins involved in the control of gene expression in eukaryotes. Although some of these proteins have been sequenced, their biochemical functions are not well understood and the identification of homologies to proteins of known activities may give useful clues to the functions of these regulatory proteins. We report here that the qa-1S repressor protein of the fungus Neurospora crassa is strongly homologous to the pentafunctional arom enzyme found in many lower eukaryotes. We believe that this is the first known case of a repressor protein that is unequivocally homologous to metabolic enzymes. These findings allow us to propose likely functions for some regions of the qa-1S protein.

Amino Acid Sequence↗
PubMed1990

Beta-D-glycosidase activities of Humicola grisea: biochemical and kinetic characterization of a multifunctional enzyme.

A beta-D-glycosidase activity was purified from mycelium of Humicola grisea var. thermoidea grown on avicel as the main carbon source. The purified enzyme was a glycoprotein and migrated as a single polypeptide band on polyacrylamide gel electrophoresis under native or denaturing conditions. The apparent molecular weight of the enzyme was estimated to be 55 kDa by gel filtration and SDS-PAGE. The enzyme was active against o-nitrophenyl beta-D-galactoside; p-nitrophenyl beta-D-glucoside, p-nitrophenyl beta-D-fucoside, lactose and cellobiose, PNP fucoside (synthetic substrate) and cellobiose (natural substrate) being the best utilized. A comparison of the properties of beta-D-galactosidase, beta-D-glucosidase and beta-D-fucosidase showed that three activities exhibited similar pH and temperature optima and the same thermostability. The hydrolysis rate of substrate mixtures suggests that the enzyme possesses a common catalytic site for all the substrates assayed.

Chromatography, Gel↗
PubMed1985

Evidence for overlapping active sites in a multifunctional enzyme: immunochemical and chemical modification studies on C1-tetrahydrofolate synthase from Saccharomyces cerevisiae.

The relationship of the active sites which catalyze the three reactions in the trifunctional enzyme C1-tetrahydrofolate synthase (C1-THF synthase) from Saccharomyces cerevisiae has been examined with immunochemical and chemical modification techniques. Immunotitration of the enzyme with a polyclonal antiserum resulted in identical inhibition curves for the dehydrogenase and cyclohydrolase activities which were distinctly different from the inhibition curve for the synthetase activity. During chemical modification with diethyl pyrocarbonate (DEPC), the three activities were inactivated at significantly different rates, indicating that at least three distinct essential residues are involved in the reaction with DEPC. The pH dependence of the reaction with DEPC was consistent with the modification of histidyl residues. Treatment of C1-THF synthase with N-ethylmaleimide (NEM) resulted in significant inactivation of only the dehydrogenase and cyclohydrolase activities, with the cyclohydrolase at least an order of magnitude more sensitive than the dehydrogenase. Inactivation of cyclohydrolase was biphasic at NEM concentrations above 0.1 mM, suggesting two essential cysteinyl residues were being modified. NADP+, a dehydrogenase substrate, protected both dehydrogenase and cyclohydrolase activities, but not synthetase activity, against inactivation by either reagent. Synthetase substrates had no protective ability. Pteroylpolyglutamates and p-aminobenzoic acid polyglutamates exhibited some protection of all three activities. The p-aminobenzoic acid polyglutamate series showed progressive protection with increasing chain length. These results are consistent with an overlapping site for the dehydrogenase and cyclohydrolase reactions, independent from the synthetase active site. Possible active-site configurations and the role of the polyglutamate tail in substrate binding are discussed.

Aminohydrolases↗
PubMed1986

Biosynthesis of cyclosporin A: partial purification and properties of a multifunctional enzyme from Tolypocladium inflatum.

An enzyme fraction most probably involved in the biosynthesis of cyclosporin A was purified 540-fold from Tolypocladium inflatum. The enzyme was capable of forming covalent enzyme-substrate complexes and catalyzed the ATP-pyrophosphate exchange reactions dependent on the unmethylated constituent amino acids of cyclosporin A. Evidence was obtained that covalent binding of substrate amino acids occurred via thioester linkage. Furthermore, the N-methylation of thio-esterified valine, leucine, and glycine residues with S-adenosyl-L-methionine was demonstrated. De novo synthesis of cyclosporin A was not observed but the formation of the diketopiperazine cyclo-(D-Ala-MeLeu) from D-alanine and L-leucine under the consumption of ATP and S-adenosyl-L-methionine. This cyclodipeptide represents a partial sequence of cyclosporin A. Molecular mass determinations revealed the enzyme activity to be lying in the range of about 700 kDa.

Carbon Radioisotopes↗
PubMed1989

Site-directed mutagenesis of yeast C1-tetrahydrofolate synthase: analysis of an overlapping active site in a multifunctional enzyme.

C1-tetrahydrofolate (THF) synthase is a trifunctional protein possessing the activities 10-formyl-THF synthetase, 5,10-methenyl-THF cyclohydrolase, and 5,10-methylene-THF dehydrogenase. The current model divides this protein into two functionally independent domains with dehydrogenase/cyclohydrolase activities sharing an overlapping active site on the N-terminal domain and synthetase activity associated with the C-terminal domain. Previous chemical modification studies on C1-THF synthase from the yeast Saccharomyces cerevisiae indicated at least two cysteinyl residues involved in the dehydrogenase/cyclohydrolase reactions [Appling, D. R., & Rabinowitz, J. C. (1985) Biochemistry 24, 3540-3547]. In the present work, site-directed mutagenesis of the S. cerevisiae ADE3 gene, which encodes C1-THF synthase, was used to individually change each cysteine contained within the dehydrogenase/cyclohydrolase domain (Cys-11, Cys-144, and Cys-257) to serine. The resulting proteins were overexpressed in yeast and purified for kinetic analysis. Site-specific mutations in the dehydrogenase/cyclohydrolase domain did not affect synthetase activity, consistent with the proposed domain structure. The C144S and C257S mutations result in 7- and 2-fold increases, respectively, in the dehydrogenase Km for NADP+. C144S lowers the dehydrogenase maximal velocity roughly 50% while C257S has a maximal velocity similar to that of the wild type. Cyclohydrolase catalytic activity is reduced 20-fold by the C144S mutation but increased 2-fold by the C257S mutation. Conversion of Cys-11 to serine has a negligible effect on dehydrogenase/cyclohydrolase activity. A double mutant, C144S/C257S, results in catalytic properties roughly multiplicative of the individual mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗