A pure enzyme catalyzing penicillin biosynthesis

Go it alone: four-electron oxidations by mononuclear non-heme iron enzymes

This review discusses the current mechanistic understanding of a group of mononuclear non-heme iron-dependent enzymes that catalyze four-electron oxidation of their organic substrates without the use of any cofactors or cosubstrates. One set of enzymes acts on α-ketoacid-containing substrates, coupling decarboxylation to oxygen activation. This group includes 4-hydroxyphenylpyruvate dioxygenase, 4-hydroxymandelate synthase, and CloR involved in clorobiocin biosynthesis. A second set of enzymes acts on substrates containing a thiol group that coordinates to the iron. This group is comprised of isopenicillin N synthase, thiol dioxygenases, and enzymes involved in the biosynthesis of ergothioneine and ovothiol. The final group of enzymes includes HEPD and MPnS that both carry out the oxidative cleavage of the carbon-carbon bond of 2-hydroxyethylphosphonate but generate different products. Commonalities amongst many of these enzymes are discussed and include the initial substrate oxidation by a ferric-superoxo-intermediate and a second oxidation by a ferryl species.

Penicillin: the medicine with the greatest impact on therapeutic outcomes

The principal point of this paper is that the discovery of penicillin and the development of the supporting technologies in microbiology and chemical engineering leading to its commercial scale production represent it as the medicine with the greatest impact on therapeutic outcomes. Our nomination of penicillin for the top therapeutic molecule rests on two lines of evidence concerning the impact of this event: (1) the magnitude of the therapeutic outcomes resulting from the clinical application of penicillin and the subsequent widespread use of antibiotics and (2) the technologies developed for production of penicillin, including both microbial strain selection and improvement plus chemical engineering methods responsible for successful submerged fermentation production. These became the basis for production of all subsequent antibiotics in use today. These same technologies became the model for the development and production of new types of bioproducts (i.e., anticancer agents, monoclonal antibodies, and industrial enzymes). The clinical impact of penicillin was large and immediate. By ushering in the widespread clinical use of antibiotics, penicillin was responsible for enabling the control of many infectious diseases that had previously burdened mankind, with subsequent impact on global population demographics. Moreover, the large cumulative public effect of the many new antibiotics and new bioproducts that were developed and commercialized on the basis of the science and technology after penicillin demonstrates that penicillin had the greatest therapeutic impact event of all times.

Regio- and stereodivergent antibiotic oxidative carbocyclizations catalysed by Rieske oxygenase-like enzymes

Oxidative cyclizations, exemplified by the biosynthetic assembly of the penicillin nucleus from a tripeptide precursor, are arguably the most synthetically powerful implementation of C-H activation reactions in nature. Here, we show that Rieske oxygenase-like enzymes mediate regio- and stereodivergent oxidative cyclizations to form 10- and 12-membered carbocyclic rings in the key steps of the biosynthesis of the antibiotics streptorubin B and metacycloprodigiosin, respectively. These reactions represent the first examples of oxidative carbocyclizations catalysed by non-haem iron-dependent oxidases and define a novel type of catalytic activity for Rieske enzymes. A better understanding of how these enzymes achieve such remarkable regio- and stereocontrol in the functionalization of unactivated hydrocarbon chains will greatly facilitate the development of selective man-made C-H activation catalysts.

Chapter 16. Enzymology of beta-lactam compounds with cephem structure produced by actinomycete

Cephamycins are beta-lactam antibiotics with a cephem structure produced by actinomycetes. They are synthesized by a pathway similar to that of cephalosporin C in filamentous fungi but the actinomycetes pathway contains additional enzymes for the formation of the alpha-aminoadipic acid (AAA) precursor and for the final steps specific to cephemycins. Most of the biochemical and genetic studies on cephemycins have been made on cephemycin C biosynthesis in the producer strains Streptomyces clavuligerus ATCC27064 and Amycolatopsis lactamdurans NRRL3802. Genes encoding cephamycin C biosynthetic enzymes are clustered in both actinomycetes. Ten enzymatic steps are involved in the formation of cephamycin C. The precursor alpha-AAA is formed by the sequential action of lysine-6-aminotransferase and piperideine-6-carboxylate dehydrogenase. Steps common to cephalosporin C biosynthesis include the formation of the tripeptide L-delta-alpha-aminoadipyl-L-cysteinyl-D-valine (ACV) by ACV synthetase, the cyclization of ACV to form isopenicillin N (IPN) by IPN synthase, the epimerization of IPN to penicillin N by isopenicillin N epimerase, the ring expansion of penicillin N to a six member cephem ring by deacetoxycephalosporin C synthase (DAOCS) and the hydroxylation at C-3' by deacetylcephalosporin C hydroxylase. However, in actinomycetes, the epimerization step is different from that in cephalosporin-producing fungi, and the expansion of the ring and its hydroxylation are performed by separate enzymes. Specific steps in cephamycin biosynthesis include the carbamoylation at C-3' by cephem carbamoyl transferase and the introduction of a methoxyl group at C-7 by the joint action of a C-7 cephem-hydroxylase and a methyltransferase. All the enzymes of the pathway have been purified almost to homogeneity and the DAOC synthase and 7-hydroxycephem-methyltransferase (CmcI) of S. clavuligerus have been crystallized giving insights into the mode of action of these enzymes. The cefE gene of S. clavuligerus, encoding DAOCS, has been extensively used to expand the penicillin ring in filamentous fungi in vivo using DNA recombinant technology.

Nonribosomal peptide synthetases involved in the production of medically relevant natural products

Natural products biosynthesized wholly or in part by nonribosomal peptide synthetases (NRPSs) are some of the most important drugs currently used clinically for the treatment of a variety of diseases. Since the initial research into NRPSs in the early 1960s, we have gained considerable insights into the mechanism by which these enzymes assemble these natural products. This review will present a brief history of how the basic mechanistic steps of NRPSs were initially deciphered and how this information has led us to understand how nature modified these systems to generate the enormous structural diversity seen in nonribosomal peptides. This review will also briefly discuss how drug development and discovery are being influenced by what we have learned from nature about nonribosomal peptide biosynthesis.

Pickles, Pectin, and Penicillin

My professional life has been devoted to the study of microbial products and their biosynthesis, regulation, and overproduction. These have included primary metabolites (glutamic acid, tryptophan, inosinic acid, guanylic acid, vitamin B(12), riboflavin, pantothenic acid, ethanol, and lactic acid) and secondary metabolites (penicillin, cephalosporins, streptomycin, fosfomycin, gramicidin S, rapamycin, indolmycin, microcin B17, fumagillin, mycotoxins, Monascus pigments, and tetramethylpyrazine). Other areas included microbial nutrition, strain improvement, bioconversions of statins and beta-lactams, sporulation and germination, plasmid stability, gel microdroplets, and the production of double-stranded RNA, the polymer xanthan, and enzymes (polygalacturonase, protease, cellulase). Most of the studies were carried out with me by devoted and hardworking industrial scientists for 15 years at Merck & Co. and by similarly characterized students, postdoctorals, and visiting scientists during my 32 years at the Massachusetts Institute of Technology. I owe much of my success to my mentors from academia and industry. My recent research activities with undergraduate students at the Charles A. Dana Research Institute for Scientists Emeriti (R.I.S.E.) at Drew University have been very rewarding and are allowing me to continue my career.

Syntheses, photophysics, and photochemistry of trinuclear copper(I) thiolate and hexanuclear copper(I) selenolate complexes: X-ray crystal structures of [Cu(6)(mu-dppm)4(mu(3)-SePh)4](BF(4))2 and [Cu(6)(mu-(Ph(2)P)(2)NH(4))(mu(3)-SePh)4](BF(4)2

A series of trinuclear copper(I) thiolate complexes, [Cu(3)(mu-dppm)(3)(mu(3)-SR)(2)]BF(4) (R = C(6)H(4)Cl-4, C(6)H(4)CH(3)-4, C(6)H(4)OCH(3)-4, C(6)H(4)(OCH(3))(2)-3,4, C(6)H(4)-benzo-15-crown-5, or (t)()Bu), [Cu(3)(mu-dppm)(3)(mu(3)-S(t)()Bu)](BF(4))(2), and [Cu(3)(mu-dppm)(3)(mu(3)-SR)(mu(3)-Cl)]BF(4) (R = C(6)H(4)CH(3)-4, C(6)H(4)(t)()Bu-4, or C(6)H(4)(CH(3))(3)-2,4,6) and two hexanuclear copper(I) selenolate complexes, [Cu(6)(mu-P(wedge)P)(4)(mu(3)-SePh)(4)](BF(4))(2) (P(wedge)P = dppm, (Ph(2)P)(2)NH), have been synthesized, and their photophysical properties have been studied. The X-ray crystal structures of both copper(I) selenolate complexes have been determined. These complexes have been shown to exhibit long-lived low-energy emission in solution, attributed to an excited state of predominantly ligand-to-metal charge-transfer [chalcogenolate to copper(I)] origin.

Molecular regulation of beta-lactam biosynthesis in filamentous fungi

The most commonly used beta-lactam antibiotics for the therapy of infectious diseases are penicillin and cephalosporin. Penicillin is produced as an end product by some fungi, most notably by Aspergillus (Emericella) nidulans and Penicillium chrysogenum. Cephalosporins are synthesized by both bacteria and fungi, e.g., by the fungus Acremonium chrysogenum (Cephalosporium acremonium). The biosynthetic pathways leading to both secondary metabolites start from the same three amino acid precursors and have the first two enzymatic reactions in common. Penicillin biosynthesis is catalyzed by three enzymes encoded by acvA (pcbAB), ipnA (pcbC), and aatA (penDE). The genes are organized into a cluster. In A. chrysogenum, in addition to acvA and ipnA, a second cluster contains the genes encoding enzymes that catalyze the reactions of the later steps of the cephalosporin pathway (cefEF and cefG). Within the last few years, several studies have indicated that the fungal beta-lactam biosynthesis genes are controlled by a complex regulatory network, e. g., by the ambient pH, carbon source, and amino acids. A comparison with the regulatory mechanisms (regulatory proteins and DNA elements) involved in the regulation of genes of primary metabolism in lower eukaryotes is thus of great interest. This has already led to the elucidation of new regulatory mechanisms. Furthermore, such investigations have contributed to the elucidation of signals leading to the production of beta-lactams and their physiological meaning for the producing fungi, and they can be expected to have a major impact on rational strain improvement programs. The knowledge of biosynthesis genes has already been used to produce new compounds.

Extraction and purification of cephalosporin antibiotics

The biologically active natural and semisynthetic cephalosporin antibiotics require proper methods of extraction and purification for their isolation and subsequent pharmacological studies. This article reviews the various methods useful for extraction and purification of individual compounds as well as the enzymes involved in their biosynthesis. Applicability of the methods for downstream processing of the spent medium has been critically analysed. Adsorption chromatography, particularly with reverse phase materials, in combination with membrane separation is the most successful technique for extraction as well as purification of most of the enzymes and individual compounds. Techniques such as reactive extraction in liquid membrane, non-dispersive extraction in hollow fiber membrane and aqueous two-phase extraction are likely to emerge in new generation processes. Finally, some aspects of process design and scale-up have been discussed, highlighting the research needs of pragmatic importance.

Genes for beta-lactam antibiotic biosynthesis

The genes pcbAB, pcbC and penDE encoding enzymes involved in the biosynthesis of penicillin have been cloned from Penicillium chrysogenum and Aspergillus nidulans. They are clustered in chromosome I (10.4 Mb) of P. chrysogenum, but they are located in chromosome II of Penicillium notatum (9.6 Mb) and in chromosome VI (3.0 Mb) of A. nidulans. Expression studies have shown that each gene is expressed as a single transcript from separate promoters. Enzyme regulation studies and gene expression analysis have provided useful information to understand the control of gene expression leading to overexpression of the genes involved in penicillin biosynthesis. Cephalosporin genes have been studied in Cephalosporium acremonium and also in cephalosporin-producing bacteria. In C. acremonium the genes involved in cephalosporin biosynthesis are separated in at least two clusters. Cluster I (pcbAB-pcbC) encodes the first two enzymes of the cephalosporin pathway which are very similar to those involved in penicillin biosynthesis. Cluster II (cefEF-cefG), encodes the last three enzymatic activities of the cephalosporin pathway. It is unknown, at this time, if the cefD gene encoding isopenicillin epimerase is linked to any of the two clusters. In cephamycin producing bacteria the genes encoding the entire biosynthetic pathway are located in a single cluster extending for about 30 kb in Nocardia lactamdurans, and in Streptomyces clavuligerus. The cephamycin clusters of N. lactamdurans and S. clavuligerus include a gene lat which encodes lysine-6-aminotransferase an enzyme involved in formation of the precursor alpha-aminoadipic acid. The N. lactamdurans cephamycin cluster includes, in addition, a beta-lactamase (bla) gene, a penicillin binding protein (pbp), and a transmembrane protein gene (cmcT) that is probably involved in secretion of the cephamycin. Little is known however about the mechanism of control of gene expression in the different beta-lactam producers. The availability of most of the structural genes provides a good basis for further studies on gene expression. This knowledge should lead in the next decade to a rational design of strain improvement procedures. The origin and evolution of beta-lactam genes is intriguing since their nucleotide sequences are extremely conserved despite their restricted distribution in the microbial world.

Expression of fungal genes involved in penicllin biosynthesis

Carbon catabolite repression and pH regulation are regulatory circuits with a wide domain of action in the Plectomycetes. Penicillin biosynthesis is one of the pathways which are under their control. The conclusions obtained so far, which are based on studies of the genetic and molecular regulation of the penicillin pathway of Aspergillus nidulans, would have been much harder to produce using an organism such as Penicillium chrysogenum (the industrial penicillin producer). However, A. nidulans and P. chrysogenum are close in terms of their phylogeny and one can reasonably predict that the conclusions about A. nidulans, which are summarized in this review and which are of unquestionable biotechnological relevance, will be extrapolable to the industrial organism.

ACV synthetase

ACV synthetase (ACVS) is the first enzyme and plays a key role in the biosynthesis of all natural penicillins and cephalosporins. The enzyme is extremely unstable and little had been known about it until recently. This article summarizes the progress in research on this enzyme, including the establishment of a cell-free assay system, stabilization, purification, characterization, and gene cloning. A possible reaction sequence for ACVS catalysis is suggested.

Purification and characterization of clavaminate synthase from Streptomyces clavuligerus: an unusual oxidative enzyme in natural product biosynthesis

A pivotal step in the biosynthetic pathway to the beta-lactamase inhibitor clavulanic acid is the conversion of proclavaminic acid to clavaminic acid in a reaction requiring Fe2+, alpha-ketoglutarate, and oxygen [Elson, S. W., Baggaley, K. H., Gillett, J., Holland, S., Nicholson, N. H., Sime, J. T., & Woroniecki, S. R. (1987) J. Chem. Soc., Chem. Commun., 1736-1738]. Clavaminate synthase, the enzyme that catalyzes this oxidative cyclization/desaturation, has been purified to homogeneity from clavulanic acid producing cells of Streptomyces clavuligerus (ATCC 27064). The enzyme behaved as a monomer during gel filtration and migrated with Mr 47,000 during denaturing gel electrophoresis. After ion-exchange FPLC two active forms of the protein were resolved that differed slightly in kinetic constants and apparent molecular weight. Kinetic comparisons with the four possible diastereomers of proclavaminate confirmed the absolute configuration of the substrate to be 2S,3R. The stoichiometry of the overall transformation was determined to be proclavaminate + 2(alpha-ketoglutarate) + 2O2----clavaminate + 2(succinate) + 2CO2 + 2H2O. In the absence of proclavaminate a slow decarboxylation of alpha-ketoglutarate to succinate and CO2 was observed in an uncoupled reaction which resulted in enzyme inactivation. Steady-state kinetic studies were undertaken for an initial description of the enzyme's catalytic cycle. The double-reciprocal plot with alpha-ketoglutarate as the variable substrate was linear; this supports the proposal that two stepwise oxidations of proclavaminate occur, each with the consumption of alpha-ketoglutarate and oxygen and the release of succinate, CO2, and H2O. The intersecting initial velocity plots obtained from pairwise variation of substrate concentrations were consistent with a sequential kinetic mechanism for the first oxidation. Similarities observed between clavaminate synthase and alpha-ketoglutarate-dependent dioxygenases argue for a common mechanism of oxygen activation. However, the nature of the interactions of the substrates in the active site of clavaminate synthase apparently redirects the conventional hydroxylase activity of dioxygenases to the construction of a strained bicyclic skeleton driven by the overall reduction of dioxygen.

Purification from Cephalosporium acremonium of the initial enzyme unique to the biosynthesis of penicillins and cephalosporins

The stability of the unstable enzyme, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase from Cephalosporium acremonium C-10, was increased 10-fold which facilitated its purification. The active enzyme was purified over 100 fold to electrophoretic homogeneity by protamine sulfate treatment, ammonium sulfate fractionation, gel filtration and hydrophobic interaction chromatography. It appears to have a minimal size of 360 kDa based on SDS-polyacrylamide gel electrophoresis.

Biosynthesis and control of β-lactam antibiotics: The early steps in the “classical” tripeptide pathway

The interaction between growth and secondary metabolism develops from physiological responses of the producer organism to its environment. Nutrients are channelled into primary growth processes or into secondary processes such as antibiotic biosynthesis by a variety of metabolic controls, the nature of which has been extensively studied in organisms producing beta-lactam antibiotics via the tripeptide, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine. In the following article we review the early stages of beta-lactam biosynthesis in fungi and actinomycetes, keeping in mind the regulation of primary pathways that provide the amino acid precursors of this group of antibiotics, as well as the regulation of the secondary pathway itself. Of special importance to organisms engaging in secondary metabolism are the control mechanisms that suppress the nonessential process during rapid growth but allow secondary metabolic genes to be expressed and resources to be diverted when environmental factors generate the appropriate biochemical signals.

Cloning and characterization of the acyl-coenzyme A: 6-aminopenicillanic-acid-acyltransferase gene of Penicillium chrysogenum

A gene, aat, encoding acyl-CoA: 6-aminopenicillanic acid acyltransferase (AAT), the last enzyme of the penicillin (Pn) biosynthetic pathway, has been cloned from the genome of Penicillium chrysogenum AS-P-78. The gene contains three introns in the 5'-region and encodes a protein of 357 amino acids with an Mr of 39,943. It complements mutants of P. chrysogenum deficient in AAT activity. The aat gene is expressed as a 1.15-kb transcript and the encoded protein appears to be processed post-translationally into two nonidentical polypeptides of 102 and 255 aa, with Mrs of 11,498 and 28,461, respectively. Three proteins of 40, 11, and 29 kDa (the last one corresponding to the previously purified AAT), were identified in extracts of P. chrysogenum. The aa sequence of the N-terminal end of the 11-kDa polypeptide matched the nucleotide (nt) sequence of the 5'-region of aat. The N-terminal end of the 29-kDa polypeptide corresponded to the sequence beginning at nt position 916 of the sequenced DNA fragment (nt 441 of aat gene). The aat gene of P. chrysogenum resembles the genes encoding Pn acylases of Escherichia coli, Proteus rettgeri and Pseudomonas sp., all of which encode two nonidentical subunits derived from a common precursor, encoded by a single open reading frame.

Beta-lactam biosynthesis in a gram-negative eubacterium: purification and characterization of isopenicillin N synthase from Flavobacterium sp. strain SC 12.154

The occurrence, localization, and extraction of isopenicillin N-synthase (IPNS) were investigated in the gram-negative low-level beta-lactam producer Flavobacterium sp. strain SC 12.154, which forms deacetoxycephalosporin and excretes the cephabacin 7-formamidocephalosporin. IPNS was detected with anti-IPNS antibodies raised against the Cephalosporium acremonium enzyme. The flavobacterium enzyme, whose molecular mass (38 kilodaltons) and cofactor requirements resemble those of the fungal and Streptomyces enzymes, is formed at the transition from growth to the stationary phase. It was extracted into the polyethylene glycol phase of a polyethylene glycol-Ficoll-dextran three-phase system and was purified by quaternary aminoethyl ion-exchange chromatography, gel filtration, covalent chromatography on cystamine-Sepharose, and fast-protein liquid chromatography on Mono Q. The enzyme was characterized with respect to sulfhydryl requirement, inhibition by disulfides and metal ions, pH and temperature dependence, and stimulation by polyethylene glycol and low Triton X-100 concentrations, as well as by several amino acids, including alpha-aminoadipic acid and cysteine. The Km for alpha-aminoadipyl-cysteinyl-D-valine was 0.08 mM. An inactive membrane-associated form of IPNS was detected together with a beta-lactamase active on isopenicillin N. The system has been suggested as a model for the study of endogenous functions of beta-lactams in bacteria.

Cloning, characterization, and expression in Escherichia coli of the Streptomyces clavuligerus gene encoding deacetoxycephalosporin C synthetase

Biosynthesis of cephalosporin antibiotics involves an expansion of the five-membered thiazolidine ring of penicillin N to the six-membered dihydrothiazine ring of deacetoxycephalosporin C by a deacetoxycephalosporin C synthetase (DAOCS) enzyme activity. Hydroxylation of deacetoxycephalosporin C to form deacetylcephalosporin C by a deacetylcephalosporin C synthetase (DACS) activity is the next step in biosynthesis of cephalosporins. In Cephalosporium acremonium, both of these catalytic activities are exhibited by a bifunctional enzyme, DAOCS-DACS, encoded by a single gene, cefEF. In Streptomyces clavuligerus, separable enzymes, DAOCS (expandase) and DACS (hydroxylase), catalyze these respective reactions. We have cloned, sequenced, and expressed in E. coli an S. clavuligerus gene, designated cefE, which encodes DAOCS but not DACS. The deduced amino acid sequence of DAOCS from S. clavuligerus (calculated Mr of 34,519) shows marked similarity (approximately 57%) to the deduced sequence of DAOCS-DACS from C. acremonium; however, the latter sequence is longer by 21 amino acid residues.

Protein purification

This monograph summarizes recent developments in the purification and analysis of natural and recombinant proteins. The basic strategies employed in protein purification are reviewed with regards to the characteristics of the protein of interest that may aid its isolation, choice of the starting material, and use of denaturants. Preparation of cell-free extracts followed by bulk precipitation and/or phase partition constitute the initial steps of many purification schemes. Chromatographic methods (size exclusion, ion exchange, hydroxylapatite, reversed phase, hydrophobic interaction and affinity based) utilizing either traditional, low pressure or high-performance liquid chromatography instrumentation are discussed. Electrophoretic techniques used to analyze the homogeneity of the protein product include SDS-PAGE, isotachophoresis, IEF and two dimensional gel electrophoresis.

Cloning and nucleotide sequence determination of the isopenicillin N synthetase gene from Streptomyces clavuligerus

The isopenicillin N synthetase (IPNS) gene from Streptomyces clavuligerus was isolated from an Escherichia coli plasmid library of S. clavuligerus genomic DNA fragments using a 44-mer mixed oligodeoxynucleotide probe. The nucleotide sequence of a 3-kb region of the cloned fragment from the plasmid, pBL1, was determined and analysis of the sequence showed an open reading frame that could encode a protein of 329 amino acids with an Mr of 36,917. When the S. clavuligerus DNA from pBL1 was introduced into an IPNS-deficient mutant of S. clavuligerus on the Streptomyces vector pIJ941, the recombinant plasmid was able to complement the mutation and restore IPNS activity. The protein coding region of the S. clavuligerus IPNS gene shows about 63% and 62% similarity to the Cephalosporium acremonium and Penicillium chrysogenum IPNS nucleotide sequences, respectively, and the predicted amino acid sequence of the encoded protein showed about 56% similarity to both fungal sequences.

Purification and initial characterization of an enzyme with deacetoxycephalosporin C synthetase and hydroxylase activities

Deacetoxycephalosporin C synthetase (expandase) from Cephalosporium acremonium (Acremonium chrysogenum) was purified to near homogeneity as judged by SDS/polyacrylamide-gel electrophoresis. The enzyme (Mr about 40,000) exhibited a pH optimum around 7.5. It required 2-oxoglutarate (Km 0.04 mM), Fe2+ and O2 as cofactors, and ascorbate and dithiothreitol were necessary for maximum activity. It was stable for over 4 weeks at -70 degrees C in the presence of 1 mM-dithiothreitol. Activity was inhibited by the thiol-quenching reagent N-ethylmaleimide, the metal-ion-chelating reagent bathophenanthroline, and NH4HCO3. The highly purified enzyme also showed deacetoxycephalosporin C hydroxylase (deacetylcephalosporin C synthetase) activity, indicating that both expandase and hydroxylase activities are properties of a single protein. These activities could not be separated by ion-exchange, dye-ligand, gel-filtration or hydrophobic chromatography. A beta-sulphoxide and a 3 beta-methylene hydroxy analogue of penicillin N were synthesized to test as potential intermediates in the ring-expansion reaction, Neither compound was a substrate for the enzyme. A synthetic analogue in which the 3 beta-methyl group and the 2-hydrogen atom of penicillin N were replaced by a cyclopropane ring was not a substrate but was a reversible inhibitor of the enzyme.

Copurification and characterization of deacetoxycephalosporin C synthetase/hydroxylase from Cephalosporium acremonium

Deacetoxycephalosporin C synthetase (expandase), which catalyzes ring expansion of penicillin N to deacetoxycephalosporin C (DAOC), has been stabilized in vitro and purified to near homogeneity from the industrially important fungus Cephalosporium acremonium. Throughout the purification, the expandase activity remained physically associated with and in a constant ratio of 7:1 to DAOC hydroxylase activity. The latter activity mediates hydroxylation of DAOC to deacetylcephalosporin C (DAC). The copurified expandase/hydroxylase appeared to be monomeric, with a molecular weight of 41,000 +/- 2,000 and an isoelectric point of 6.3 +/- 0.3. Both catalytic activities required alpha-ketoglutarate, Fe2+, and O2 and were stimulated by ascorbate, dithiothreitol, and ATP. The Fe2+ requirement was specific, and sulfhydryl groups in the purified protein were apparently essential for both ring expansion and hydroxylation. The kinetics and stoichiometry of DAOC/DAC formation from the expandase/hydroxylase-catalyzed reactions suggested that ring expansion of penicillin N preceded hydroxylation of DAOC.

Cloning and characterization of the isopenicillin N synthetase gene mediating the formation of the beta-lactam ring in Aspergillus nidulans

Genomic clones containing an Aspergillus nidulans isopenicillin N synthetase (IPNS) gene have been identified by heterologous hybridization with a Cephalosporium acremonium DNA probe. The open reading frame encodes a 331 amino acid polypeptide with extensive homology with the genes of other beta-lactam-producing fungi. The gene product has been overexpressed in Escherichia coli and shown to have activity of IPNS. This represents the first evidence at the molecular level that the biosynthesis of penicillins in A. nidulans occurs by the same pathway as in other beta-lactam-producing microorganisms. Comparison of available nucleotide sequences from IPNS genes suggests a horizontal transmission of the gene between the prokaryotic beta-lactam producers of the genus Streptomyces and the filamentous fungi.

Isolation, sequence determination and expression in Escherichia coli of the isopenicillin N synthetase gene from Cephalosporium acremonium

The enzyme isopenicillin N synthetase (IPS) catalyses the oxidative condensation of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (LLD-ACV) to isopenicillin N, which is a central reaction in the pathway to clinically important penicillins and cephalosporins. Here we report the cloning, characterization and expression in Escherichia coli of the gene encoding the IPS protein in Cephalosporium acremonium. The IPS gene was identified by purifying IPS protein, determining the first 23 amino-terminal amino acids, preparing a set of synthetic oligonucleotides encoding a portion of the determined amino-acid sequence, and probing a cosmid genome library with the mixed oligonucleotides. A cosmid hybridizing with the probe was isolated and the IPS gene was localized and sequenced. The IPS gene encodes a polypeptide of relative molecular mass (Mr) 38,416. When this open reading frame was cloned into an E. coli expression vector and inserted into E. coli, the recombinant E. coli produced a new protein co-migrating with authentic IPS as the major protein of the cell (approximately 20% of cell protein). Crude cell extracts condensed LLD-ACV to a penicillinase-sensitive molecule whose antibacterial activity indicated that it was isopenicillin N.

N-terminal amino acid sequence and some properties of isopenicillin-N synthetase from Cephalosporium acremonium

Isopenicillin-N synthetase (IPNS) was purified to homogeneity from Cephalosporium acremonium C0728. The enzyme existed in two states during purification; an oxidised state with a disulphide linkage and its reduced state. These two forms can be interconverted in the presence or absence of thiol agents, and separated by fast protein liquid chromatography (FPLC) with the strong anion exchange Mono-Q column. The enzyme is a monomer with a molecular mass of 38 kDa and pI 5.05. The first 50 amino acid N-terminal sequence of the enzyme was determined. The purified enzyme has an absolute requirement of Fe2+ and a 2-electron donor for activity.