Expression of genes and processing of enzymes for the biosynthesis of penicillins and cephalosporins
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- Martín, J.F., Gutiérrez, S., Fernández, F.J. et al. Antonie van Leeuwenhoek (1994) 65: 227. doi:10.1007/BF00871951
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The genespcbAB,pcbC andpenDE encoding the enzymes (α-aminoadipyl-cysteinyl-valine synthetase, isopenicillin N synthase and isopenicillin N acyltransferase, respectively) involved in the biosynthesis of penicillin have been cloned fromPenicillium chrysogenum andAspergillus nidulans. They are clustered in chromosome I (10.4 Mb) ofP. chrysogenum, in chromosome II ofPenicillium notatum (9.6 Mb) and in chromosome VI (3.0 Mb) ofA. nidulans. 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 genes involved in penicillin biosynthesis. The enzyme isopenicillin N acyltransferase encoded by thepenDE gene is synthesized as a 40 kDa protein that is (self)processed into two subunits of 29 and 11 kDa. Both subunits appear to be required for acyl-CoA 6-APA acyltransferase activity. The isopenicillin N acyltransferase was shown to be located in microbodies, whereas the isopenicillin N synthase has been reported to be present in vesicles of the Golgi body and in the cell wall. A mutant in the carboxyl-terminal region of the isopenicillin N acyltransferase lacking the three final amino acids of the enzymes was not properly located in the microbodies and failed to synthesize penicillin in vivo. InC. acremonium the genes involved in cephalosporin biosynthesis are separated in at least two clusters. Cluster I (pcbAB-pcbC) encodes the first two enzymes (α-aminoadipyl-cysteinyl valine synthetase and isopenicillin N synthase) of the cephalosporin pathway which are very similar to those involved in penicillin biosynthesis. Cluster II (cefEF-cefG), encodes the last three enzymatic activities (deacetoxycephalosporin C synthetase/hydroxylase and deacetylcephalosporin C acetyltransferase) of the cephalosporin pathway. It is unknown, at this time, if thecefD gene encoding isopenicillin epimerase is linked to any of these two clusters. Methionine stimulates cephalosporin biosynthesis in cultures of three different strains ofA. chrysogenum. Methionine increases the levels of enzymes (isopenicillin N synthase and deacetylcephalosporin C acetyltransferase) expressed from genes (pcbC andcefG respectively) which are separated in the two different clusters of cephalosporin biosynthesis genes. This result suggests that both clusters of genes have regulatory elements which are activated by methionine. Methionine-supplemented cells showed higher levels of transcripts of thepcbAB,pcbC,cefEF genes and to a lesser extent ofcefG than cells grown in absence of methionine. The levels of thecefG transcript were very low as compared to those ofpcbAB,pcbC andcefEF. The induction by methionine of transcription of the four cephalosporin biosynthesis genes and the known effect of this amino acid on differentiation ofA. chrysogenum indicates that methionine exerts a pleiotropic effect that regulates coordinately cephalosporin biosynthesis and differentiation.