Cloning of a Streptomyces clavuligerus DNA fragment encoding the cephalosporin 7 alpha-hydroxylase and its expression in Streptomyces lividans

Abstract

A 26-mer DNA probe was designed from N-terminal sequence data for the cephalosporin 7a-hydroxylase (CH) of Streptomyces clavuligerus NRRL 3585 and used to screen a DNA library from this organism. The library was constructed in the AGEM-1l phage system. After plaque purification and reprobing, positive recombinant phages were chosen for further analysis. Characterization of the cloned DNA by restriction mapping and Southern hybridization showed that a 1.5-kb SailI fragment hybridized to the probe. Polymerase chain reaction assays using this fragment as a template and the probe as a primer indicated that the fragment carries the entire putative CH gene (cmcl). This was confirmed through the expression of CH enzymatic activity when the fragment was introduced into Streptomyces lividans. A putative 13-lactamase activity was detected in S. lividans.Some actinomycetes produce 7a-methoxylated cephalosporins, which are named cephamycins. Methoxylation of cephalosporins increases their inhibitory effect on transpeptidase(s) involved in bacterial cell wall synthesis (7) and reduces inactivation by 3-lactamases (2), making the cephamycins important clinical antibiotics. As a representative of cephamycins, cephamycin C exhibits activity against many cephalosporin-resistant bacteria (11). The cephalosporinproducing fungi and the cephamycin-producing actinomycetes share a biosynthetic pathway from L-a-aminoadipate, L-cysteine, and L-valine to deacetylcephalosporin C (3). However, the cephalosporin-producing fungi lack the methoxylation system to convert cephalosporins into cephamycins. Many, if not all, biosynthetic genes involved in the common pathway have been cloned from fungi and actinomycetes. The cloning of the genes for cyclase, epimerase, expandase, and deacetoxycephalosporin C hydroxylase has been reviewed elsewhere (14). More recently, the cloning of the oa-aminoadipyl-cysteinyl-valine (ACV) synthetase gene from Cephalosporium acremonium has also been reported (4, 10). On the other hand, the cloning of the individual genes involved in 7a-methoxylation of cephalosporins has not been reported, although Chen et al. (1) have described the cloning and expression of a cluster of genes for cephamycin C production from Streptomyces cattleya in the nonproducer Streptomyces lividans. Streptomyces clavuligerus cell-free enzymatic reactions indicate that methoxylation by actinomycetes occurs in two steps (8,12,18). The first step is the hydroxylation of cephalosporin at C-7, and the second step is methylation. Cephalosporin 7a-hydroxylase (CH), which catalyzes the first step, was purified to near homogeneity from S. clavuligerus NRRL 3585 (19). In the present study, using a degenerate mixed-oligonucleotide probe designed * Corresponding author.

The enzymes of β-lactam biosynthesis

“…22). 109 CmcI was initially annotated as a cephalosporin hydroxylase, 333 but no evidence for Fe II /2OG binding could be found. 109 Despite its low sequence identity (8-23%) to SAM-dependent methyltransferases, the CmcI structure is related to that of catechol Omethyltransferase with overlapping nucleotide-binding residues.…”

A two-protein component 7 alpha-cephem-methoxylase encoded by two genes of the cephamycin C cluster converts cephalosporin C to 7-methoxycephalosporin C

“…A DNA fragment based on the amino-terminal end of the purified 7-cephem hydroxylase was cloned recently from S. clavuligerus (20). However, when the DNA fragment was expressed in S. lividans, little 7-cephem hydroxylase was observed despite the gene amplification, compared with the strong activity formed from the chromosomal S. clavuligerus gene.…”

“…For many years, it has been unclear whether the C-7 hydroxylase of the cephamycin pathway is different from the C-3Ј hydroxylase which converts deacetoxycephalosporin C into deacetylcephalosporin C. Demain and coworkers (21) purified the 7-cephem hydroxylase activity of S. clavuligerus, which was different from the C-3Ј hydroxylase (20).…”