Ho

Mederrhodin

OH O Mederrhodin

Fig. 3.34. (a) Structure of actinorhodin, (b) structure of medermycin, (c) structure of mederrhodin (Hunter and Baumberg, 1989).

OH O Mederrhodin

Fig. 3.34. (a) Structure of actinorhodin, (b) structure of medermycin, (c) structure of mederrhodin (Hunter and Baumberg, 1989).

the subsequent modification reactions which occur after cyclization. McDaniel et al. (1993) have constructed plasmids coding for recombinant PKSs and achieved expression in Streptomyces coelicolor. Five novel polyketides were synthesized and the system shows great promise for the production of new, potentially valuable, compounds as well as providing carbon skeletons amenable to derivatization by organic chemists.

A commercially relevant example is provided by the Lilly Research Laboratories group (Beckman et al., 1993) who produced a strain of Pénicillium chiyso-genum capable of accumulating deacetoxycephalo-sporin C (DAOC), a compound which can be biotrans-formed into 7-aminodesacetoxycephalosporanic acid

OH OH O Me

OH OH O Me

Granaticin
Dihydrogranaticin

Dihydrogranatirhodin

Fig. 3.35. (a) Structure of granaticin, (b) structure of dihydrogranaticin, (c) structure of dihydrogranatirhodin (Hunter and Baumberg, 1989).

Dihydrogranatirhodin

Fig. 3.35. (a) Structure of granaticin, (b) structure of dihydrogranaticin, (c) structure of dihydrogranatirhodin (Hunter and Baumberg, 1989).

(7ADAOC) which is a precursor of at least three chemically synthesized clinically important cephalosporins. The conventional route to 7ADAOC is by the chemical ring expansion of benzylpenicillin which is far more complex than the biotransformation of DAOC.

DAOC is produced as an intermediate in the synthesis of cephalosporin C by Cephalosporium acremonium, as shown in Fig. 3.33. However, it would be very difficult to manufacture the compound from C. acremonium by blocking the conversion of DAOC to deacetylcephalosporin C because a single bifunctional enzyme catalyses both the conversion of penicillin N to DAOC (expandase activity) and the hydroxylation of DAOC to deacetylcephalosporin C (hydroxylase activity). The bifunctional protein is encoded by the gene cef EF. In Streptomyces clavuligerus the expandase and hydroxylase enzymes are separate proteins encoded by the genes cef E and cef F respectively. Thus, 5 clavuligerus could be modified for the commercial pro duction of DAOC. However, the Lilly group did not have a strain capable of producing high cephalosporin levels available to them, but they did have a PenicilliUm chrysogenum that overproduced isopenicillin N (IPN) as an intermediate in Phenoxymethylpenicillin synthesis as shown in Fig. 3.36. Thus, to enable the Pénicillium to produce DAOC the insertion of two genes was necessary, i.e. those encoding isopenicillin epimerase and expandase. These workers had already cloned ce/E (coding for expandase) from S. clavuligerus and ce/D (coding for epimerase) from S. lipmanii. Thus, using sophisticated vector technology a P. chrysogenum was transformed with a plasmid containing both cef D and cef E. One of the isolated transformants was capable of synthesizing up to 2.5 g dm"3 DAOC and both the cef D and cef E genes were integrated into the organism's genome.

Thus, the recombinant produced by the Lilly group contained a branched biosynthetic pathway giving rise to the two end products, DAOC and Phenoxymethylpenicillin. However, the conversion of IPN to DAOC in the recombinant represented less that 10% of the conversion of IPN to Phenoxymethylpenicillin in the parent. Thus, the recombinant may still be developed to improve the productivity. These developments could involve the screening of a larger population of transformants to find one where integration of the inserted genes occurred at sites not associated with penicillin synthesis. Also, the isolation of a strain blocked in the conversion of IPN to Phenoxymethylpenicillin should give improved DAOC production.

L-u-aminoadipic acid + L-cysteinc+ L -valine 1

Isopenicillin N

Phenoxymethylpenicillin Penicillin N

Vinegar For Your Health

Vinegar For Your Health

A resource for the many ways you can use Vinegar to improve your health! In today's society of miracle medicine, we often overlook things that have been around hundreds of years! Things like Vinegar!

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