THE THIOREDOXIN SYSTEM OF PENICILLIUM-CHRYSOGENUM AND ITS POSSIBLE ROLE IN PENICILLIN BIOSYNTHESIS

Penicilliunm chrysogenum is an important producer of penicillin antibi otics. A key step in their biosynthesis is the oxidative cyclization o f delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) to isopenicil lin N by the enzyme isopenicillin N synthase (IPNS). bis ACV, the oxid ized disulfide form of ACV is, however, not a substrate for IPNS. We r eport here the characterization of a broad-range disulfide reductase f rom P. chrysogenum that efficiently reduces bis-ACV to the thiol monom er. When coupled in vitro with IPNS, it converts bis-ACV to isopenicil lin N and may therefore play a role in penicillin biosynthesis. The di sulfide reductase consists of two protein components, a 72-kDa NADPH-d ependent reductase, containing two identical subunits, and a 12-kDa ge neral disulfide reductant. The latter reduces disulfide bonds in low-m olecular-weight compounds and in proteins. The genes coding for the re ductase system were cloned and sequenced. Both possess introns. A comp arative analysis of their predicted amino acid sequences showed that t he 12-kDa protein shares 26 to 60% sequence identity with thioredoxins and that the 36-kDa protein subunit shares 44 to 49% sequence identit y with the two known bacterial thioredoxin reductases. In addition, th e P. chrysogenum NADPH-dependent reductase is able to accept thioredox in as a substrate. These results establish that the P. chrysogenum bro ad range disulfide reductase is a member of the thioredoxin family of oxidoreductases. This is the first example of the cloning of a eucaryo tic thioredoxin reductase gene.