Search PubMed⌕ Search

Biomedical subjects

H Kleinkauf

Publications and source records attributed to H Kleinkauf.

At least 37 records · Page 2Linked to original sources
PubMed1994

Purification and characterization of eucaryotic alanine racemase acting as key enzyme in cyclosporin biosynthesis.

A specific alanine racemase, which is a key enzyme in the biosynthesis of the undecapeptide cyclosporin A, was purified to electrophoretic homogeneity from the fungus Tolypocladium niveum. This is the first enzyme of this kind isolated from a eucaryotic organism. The enzyme catalyzes the reversible racemization of alanine and requires pyridoxal phosphate as the exclusive cofactor. Km values for L- and D-alanine were found to be 38 and 2 mM, respectively. Maximal reaction velocity was observed at 42 degrees C and pH 8.8 for the L to D direction. Molecular mass determinations of the denatured enzyme by SDS-polyacrylamide gel electrophoresis gave a value of 37 kDa, whereas gel filtration calibration studies yielded a value between 120 and 150 kDa, indicating an oligomeric native structure.

Alanine Racemase↗
PubMed1994

Mechanism of cyclosporin A biosynthesis. Evidence for synthesis via a single linear undecapeptide precursor.

Cyclosporin A is synthesized by cyclosporin synthetase, a multienzyme polypeptide. This enzyme catalyzes at least 40 reaction steps in an assembly belt-like mechanism. It activates all constituent amino acids of cyclosporin A to thioesters via amino acyladenylates and carries out specific N-methylation reactions. During elongation, the activated amino acids are linked by peptide bonds leading to enzyme-bound nascent peptide chains. Some of the linear peptides of the growing cyclosporin A chain were isolated and their N-terminal amino acid was determined. D-Alanine at position 8 of the cyclosporin A molecule was found to be a starting amino acid in the biosynthetic process of cyclosporin A formation. Four intermediate peptides of the growing peptide chain of cyclosporin A could be isolated and identified. All of them represent partial sequences of cyclosporin A starting with D-alanine. That these intermediate peptides were bound by thioester linkage to cyclosporin synthetase could be demonstrated by liberation of the peptides with performic acid. The peptides strongly suggest the stepwise synthesis of a single linear peptide precursor of cyclosporin A.

2,2'-Dipyridyl↗
PubMed1993

Delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase, the multienzyme integrating the four primary reactions in beta-lactam biosynthesis, as a model peptide synthetase.

ACV synthetase forms the tripeptide precursor of penicillins and cephalosporins from alpha-aminoadipate, cysteine, and valine. Catalytic sites for substrate carboxyl activation as adenylates, peptide bond formations, epimerization and release of the tripeptide-thioester are integrated in multifunctional enzymes of 405 to 425 kD. These have been characterized from several pro- and eukaryotic beta-lactam producers. Implications of these results for the thio-template mechanism of peptide formation are discussed, as well as the use of this multienzyme as a model system for enzymatic peptide synthesis.

Amino Acid Sequence↗
PubMed1992

Two new cyclophilins from Fusarium sambucinum and Aspergillus niger: resistance of cyclophilin/cyclosporin A complexes against proteolysis.

Two new peptidyl-prolyl-cis/trans-isomerases were purified to homogeneity from Fusarium sambucinum and Aspergillus niger. They belong to the class of cyclosporin A binding proteins (cyclophilins) and have molecular masses of about 18 kDa. As has been shown for other cyclophilins, the isomerase activity of the enzymes is inhibited by cyclosporin A in the nanomolar range. Furthermore binding of cyclosporin A prevents proteolytic digestion of the cyclophilin/cyclosporin complexes by the endoproteases GluC, LysC and alpha-chymotrypsin, in contrast to the free cyclophilins, which are readily cleaved by these proteases. We could also observe this protection for cyclophilins from sheep thymus and from the cyclosporin producing fungus Tolypocladium inflatum.

Amino Acid Isomerases↗
PubMed1992

Cyclosporin synthetase is a 1.4 MDa multienzyme polypeptide. Re-evaluation of the molecular mass of various peptide synthetases.

The earlier determined molecular mass of 0.8 MDa for the multifunctional polypeptide, cyclosporin synthetase, was re-evaluated by SDS-PAGE and CsCl density gradient centrifugation. In SDS-PAGE, new molecular mass values as standards were available from sequencing data. In the CsCl density gradient extremely low protein concentrations, such as 10-50 nM could be analysed due to the fluorescence detection system of the analytical ultracentrifuge. Both methods yielded approximately the same value of about 1.4 MDa. Using this molecular mass of cyclosporin synthetase as a reference the molecular masses of various related enzymes could be re-evaluated in SDS-PAGE. The sedimentation coefficient of 26.3 S for cyclosporin synthetase indicates an oblate overall shape of the enzyme.

Cesium↗
PubMed1992

A highly specific D-hydroxyisovalerate dehydrogenase from the enniatin producer Fusarium sambucinum.

A highly specific D-hydroxyisovalerate (D-HIV) dehydrogenase, which is a key enzyme in depsipeptide synthesis, was purified to near homogeneity from the enniatin-producing fungus Fusarium sambucinum. The enzyme catalyzes the reversible reaction of 2-ketoisovalerate (2-KIV) to D-HIV. It is strictly dependent on NADPH and exhibits a high substrate specificity with respect to 2-KIV. NADH was not accepted by the enzyme. Km values for 2-KIV and NADPH were found to be 200 and 333 microM, respectively. D-HIV dehydrogenase consists of a single polypeptide chain with a molecular mass of about 53 kDa. Optimum temperature for the reduction of 2-KIV was 35 degrees C and for the oxidation reaction was 45 degrees C. The optimum pH was found to be 7 for the reduction and 8-9 for the oxidation reaction.

Alcohol Oxidoreductases↗
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↗
PubMed1992

[Biosynthesis of peptides: a non-ribosomal system].

The biosynthesis of peptides in nonribosomal systems is accomplished by complex multienzymes. These multienzymes assemble the required template for the construction of each natural product in the form of linearly coupled modules. This organization principle permits the integration of multistep synthetic processes on a single macromolecule.

Amino Acid Sequence↗
PubMed1992

Enzymatic biosynthesis of cyclosporin A and analogues.

The final assembly of the undecapeptide chain of cyclosporin A and its cyclization is accomplished in Beauveria nivea by cyclosporin synthetase. This multienzyme is the largest integrated enzyme structure so far reported. Its size has been estimated at approximately 1,400 kDa by two different methods: 1), by 3% SDS-PAGE using the related multienzymes ACV synthetase and gramicidin S synthetase 2 as references (420 and 556 kDa, respectively); and 2), by CsCl density gradient centrifugation experiments using fluorescence-labeled cyclosporin synthetase. Besides cyclosporin A and a number of cyclosporins known from fermentation studies cyclosporin synthetase is capable of synthesizing some new cyclosporins which are so far unobtainable by fermentation. So, for example the synthesis of [N-methyl-(+)-2-amino-3-hydroxy-4,4-dimethyloctanoic acid1]CyA, dihydro-CyA, [L-norvaline2,5, N-methyl-L-norvaline11]CyA, [L-allo-isoleucine5, N-methyl-L-allo-isoleucine11]CyA, [D-2-aminobutyric acid8]CyA, [beta-chloro-D-alanine8]CyA and some related compounds could be established. By using a related but different enzyme from Cylindrotrichum Bonorden, the peptolide [L-threonine2, L-leucine5,10, D-2-hydroxyisovaleric acid8]CyA could be synthesized in vitro. We were able to synthesize these cyclosporins in sufficient quantities to examine their structure by FAB mass spectroscopy and explore their immunosuppressivity. It was found that all new cyclosporins so far synthesized in the in vitro system are immunosuppressive.

Amino Acid Sequence↗
PubMed1992

Enniatin synthetases from different fusaria exhibiting distinct amino acid specificities.

Enniatin synthetases from the cyclodepsipeptide producers Fusarium lateritium and Fusarium sambucinum were purified to homogeneity and characterized. Like the previously described enniatin synthetase from Fusarium scirpi both enzymes consist of a single polypeptide chain and are very similar concerning their Mr (250 kdaltons) and reaction mechanism. Limited proteolytic digests show only slight differences in their patterns in SDS-gels. Interestingly the synthetases differ in their amino acids specificities. The enzyme from the enniatin A producer F. sambucinum exhibits a high affinity to the substrate amino acids L-Leu and L-Ile. In contrast the synthetase from the enniatin B producer F. lateritium preferably accepts L-Val, the constituent amino acid of enniatin B.

Antibodies, Monoclonal↗
PubMed1991

Cell-free biosynthesis of cyclosporin A and analogues.

The final assembly of the 11-peptide chain of cyclosporins and its cyclization is accomplished in the producer Beauveria nivea by cyclosporine synthetase. This multienzyme represents the largest integrated enzyme structure reported so far. Its size has been estimated to approximately 1,500 kDa by SDS-PAGE. Some enzyme bound linear peptides could be isolated and identified. All of them represent partial sequences of cyclosporin A starting with D-alanine. These peptides were bound by thioester linkage to the enzyme. This could be demonstrated by liberation of the peptides with performic acid and by inhibition of in vitro cyclosporin A synthesis with thiol blocking agents. Cyclosporin synthetase is capable to synthesize besides a lot of cyclosporins known from fermentation studies some new cyclosporins so far not obtainable by fermentation. So, for example the synthesis of [N-methyl-(+)-2-amino-3-hydroxy-4,4-dimethyloctanoic acid1]CyA, Dihydro-CyA, [L-norvaline2,5, N-methyl-L-norvaline11]CyA, [L-allo-isoleucine5, N-methyl-L-allo-isoleucine11]CyA, [D-2-aminobutyric acid8]CyA, [beta-chloro-D-alanine8]CyA and some related compounds could be established. We were able to synthesize these cyclosporins in sufficient quantities to ensure their structure by fast atom bomdardment mass spectroscopy and to examine their immunosuppressitivity. All new cyclosporins synthesized in the in vitro system so far are immunosuppressive.

Amino Acid Sequence↗
PubMed1990

Nonribosomal biosynthesis of peptide antibiotics.

Peptide antibiotics are known to contain non-protein amino acids, D-amino acids, hydroxy acids, and other unusual constituents. In addition they may be modified by N-methylation and cyclization reactions. Their biosynthetic origin has been connected in many cases to an enzymatic system referred to as the 'thiotemplate multienzymic mechanism'. This mechanism includes the activation of the constituent residues as adenylates on the enzymic template, the acylation of specific template thiol groups, epimerization or N-methylation at this thioester stage, and polymerization in the sequence directed by the multienzymic structure with the aid of 4'-phosphopantetheine as a cofactor, including possible cyclization or terminal modification reactions. The reaction sequences leading to gramicidin S, tyrocidine, cyclosporine, bacitracin, polymyxin, actinomycin, enniatin, beauvericin, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine and linear gramicidin are discussed. The structures of the multienzymes, their genetic organization, the biological functions of these peptides and results on related systems are discussed.

Amino Acid Sequence↗
PubMed1990

Antibiotics--cloning of biosynthetic pathways.

Biosynthetic pathways leading to antibiotics have often been found to be clustered, and new organizational forms of multifunctional enzymes have been discovered. Such polyenzymes accomplish the synthesis of complex metabolites such as peptides or polyketides by a sequence of enzymatic reactions. So, reactions leading to the tripeptide precursor of beta-lactam antibiotics, ACV, or to the cycloundecapeptide cyclosporine have been fused into single polypeptide chain synthetases, respectively. In certain isofunctional sites restricted similarities have been detected.

Anti-Bacterial Agents↗
PubMed1990

Isolation and partial characterization of cyclosporin synthetase from a cyclosporin non-producing mutant of Beauveria nivea.

Cyclosporin synthetase was isolated from a cyclosporin non-producing mutant of Beauveria nivea, strain YP 582. The enzyme has a molecular mass in the range of active cyclosporin synthetase and also contains 4'-phosphopantetheine as a prosthetic group. It is able to activate all constituent amino acids of cyclosporin A as thioesters and to carry out specific N-methylation reactions. Overall synthesis of the undecapeptide cyclosporin A in the presence of all necessary substrates was not observed, but the formation of the diketopiperazine cyclo-(D-alanyl-N-methyl-leucyl). This diketopiperazine represents a partial sequence of the cyclosporin molecule. It could be detected in the mycelium of the non-producing strain, whereas mycelium of the producing strain 7939/45 did not contain this compound. The results suggest that the inability of this mutant to produce cyclosporin A is caused by a mutation of the polypeptide chain of cyclosporin synthetase.

Amino Acid Sequence↗
PubMed1989

delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase from Aspergillus nidulans. The first enzyme in penicillin biosynthesis is a multifunctional peptide synthetase.

A multienzyme catalyzing the formation of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine, the first free intermediate in penicillin biosynthesis, was detected in an assay measuring the formation of tripeptide from L-[U-14C]valine in the presence of L-alpha-aminoadipic acid, L-cysteine, ATP, Mg2+ ions, and dithioerythritol. Enzyme was extracted from dry mycelium using a buffer with a high glycerol concentration and thiol protective agent to stabilize enzyme activity. In five steps the enzyme was purified 118-fold. It catalyzed ATP-pyrophosphate exchange in dependence of all three constituent amino acids, and the enzyme could be amino-acylated with L-[14C]valine. The molecular weight of the protein both native (in gel filtration chromatography) and denatured (polyacrylamide gel electrophoresis) was about 220 kDa. These data suggest that delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase consists of a single polypeptide chain and a multienzyme thiotemplate mechanism for the reaction sequence is postulated.

Aspergillus nidulans↗
PubMed1989

Regulation by dibutyryl cyclic AMP of carnosine synthesis in astroglia-rich primary cultures kept in serum-free medium.

The synthesis of carnosine (beta-Ala-His) by astroglia-rich primary cultures was much higher if the cells were cultivated in Ham's nutrient mixture F-12 than if they were grown in Dulbecco's modified Eagle's medium. Carnosine synthesis was not affected by the presence of insulin, transferrin, phorbol myristate acetate, or dexamethasone. However, dibutyryl cyclic AMP and other agents that can, directly or indirectly, activate cyclic AMP-dependent protein kinases strongly lower the rate of carnosine synthesis. The depression of carnosine synthesis was dependent on the concentration of dibutyryl cyclic AMP. The effect was maximal (approximately 80% inhibition) in cultures preincubated with 1 mM dibutyryl cyclic AMP for 4 days. The adenylate cyclase activator forskolin, the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, and 8-bromo-cyclic AMP caused the same depression as dibutyryl cyclic AMP, whereas neither butyrate nor dibutyryl cyclic GMP elicited any effect.

1-Methyl-3-isobutylxanthine↗