Improved expression of a hybrid Streptomyces clavuligerus cefE gene in Penicillium chrysogenum

Engineering deacetoxycephalosporin C synthase as a catalyst for the bioconversion of penicillins

7-aminodeacetoxycephalosporanic acid (7-ADCA) is a key intermediate of many clinically useful semisynthetic cephalosporins that were traditionally prepared by processes involving chemical ring expansion of penicillin G. Bioconversion of penicillins to cephalosporins using deacetoxycephalosporin C synthase (DAOCS) is an alternative and environmentally friendly process for 7-ADCA production. Arnold Demain and co-workers pioneered such a process. Later, protein engineering efforts to improve the substrate specificity and catalytic efficiency of DAOCS for penicillins have been made by many groups, and a whole cell process using Escherichia coli for bioconversion of penicillins has been developed.

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.

Combining Classical, Genetic, and Process Strategies for Improved Precursor-Directed Production of 6-Deoxyerythronolide B Analogues

A process for the production of erythromycin aglycone analogues has been developed by combining classical strain mutagenesis techniques with modern recombinant DNA methods and traditional process improvement strategies. A Streptomyces coelicolor strain expressing the heterologous 6-deoxyerythronolide B (6-dEB) synthase (DEBS) for the production of erythromycin aglycones was subjected to random mutagenesis and selection. Several strains exhibiting 2-fold higher productivities and reaching >3 g/L total macrolide aglycones were developed. These mutagenized strains were cured of the plasmid carrying the DEBS genes and a KS1 degrees mutant DEBS operon was introduced for the production of novel analogues when supplemented with a synthetic diketide precursor. The strains expressing the mutant DEBS were screened for improved 15-methyl-6-dEB production, and the best clone, strain B9, was found to be 50% more productive as compared to the parent host strain used for 15-methyl-6-dEB production. Strain B9 was evaluated in 5-L fermenters to confirm productivity in a scalable process. Although peak titers of 0.85 g/L 15-methyl-6-dEB by strain B9 confirmed improved productivity, it was hypothesized that the low solubility of 15-methyl-6-dEB limited productivity. The solubility of 15-methyl-6-dEB in water was determined to be 0.25-0.40 g/L, although higher titers are possible in fermentation medium. The incorporation of the hydrophobic resin XAD-16HP resulted in both the in situ adsorption of the product and the slow release of the diketide precursor. The resin-containing fermentation achieved 1.3 g/L 15-methyl-6-dEB, 50% higher than the resin-free process. By combining classical mutagenesis, recombinant DNA techniques, and process development, 15-methyl-6-dEB productivity was increased by over 100% in a scalable fermentation process.

Environmentally safe production of 7-aminodeacetoxycephalosporanic acid (7-ADCA) using recombinant strains of Acremonium chrysogenum

Medically useful semisynthetic cephalosporins are made from 7-aminodeacetoxycephalosporanic acid (7-ADCA) or 7-aminocephalosporanic acid (7-ACA). Here we describe a new industrially amenable bioprocess for the production of the important intermediate 7-ADCA that can replace the expensive and environmentally unfriendly chemical method classically used. The method is based on the disruption and one-step replacement of the cefEF gene, encoding the bifunctional expandase/hydroxylase activity, of an actual industrial cephalosporin C production strain of Acremonium chrysogenum. Subsequent cloning and expression of the cefE gene from Streptomyces clavuligerus in A. chrysogenum yield recombinant strains producing high titers of deacetoxycephalosporin C (DAOC). Production level of DAOC is nearly equivalent (75-80%) to the total beta-lactams biosynthesized by the parental overproducing strain. DAOC deacylation is carried out by two final enzymatic bioconversions catalyzed by D-amino acid oxidase (DAO) and glutaryl acylase (GLA) yielding 7-ADCA. In contrast to the data reported for recombinant strains of Penicillium chrysogenum expressing ring expansion activity, no detectable contamination with other cephalosporin intermediates occurred.