Genome Mining in Streptomyces. Discovery of an Unprecedented P450-Catalyzed Oxidative Rearrangement That Is the Final Step in the Biosynthesis of Pentalenolactone

The penM and pntM genes from the pentalenolactone biosynthetic gene clusters of Streptomyces exfoliatus UC5319 and Streptomyces arenae TU469 were predicted to encode orthologous cytochrome P450s, CYP161C3 and CYP161C2, responsible for the final step in the biosynthesis of the sesquiterpenoid antibiotic pentalenolactone (1). Synthetic genes optimized for expression in Escherichia coli were used to obtain recombinant PenM and PntM, each carrying an N-terminal His(6)-tag. Both proteins showed typical reduced-CO UV maxima at 450 nm, and each bound the predicted substrate, pentalenolactone F (4), with K-D values of 153 +/- 14 and 126 +/- 11 mu M for PenM and PntM, respectively, as determined by UV shift titrations. PenM and PntM both catalyzed the oxidative rearrangement of 4 to 1 when incubated in the presence of NADPH, spinach ferredoxin, ferredoxin reductase, and O-2. The steady-state kinetic parameters were k(cat) = 10.5 +/- 1.7 min(-1) and K-m = 340 +/- 100 mu M 4 for PenM and k(cat) = 8.8 +/- 0.9 min(-1) and K-m = 430 100 mu M 4 for PntM. The in vivo function of both gene products was confirmed by the finding that the corresponding deletion mutants S. exfoliatus/Delta penM ZD22 and S. arenae/Delta pntM ZD23 no longer produced pentalenolactone but accumulated the precursor pentalenolactone F. Complementation of each deletion mutant with either penM or pntM restored production of antibiotic 1. Pentalenolactone was also produced by an engineered strain of Streptomyces avermitilis that had been complemented with pntE, pntD, and either pntM or penM, as well as the S. avermitilis electron-transport genes for ferredoxin and ferrodoxin reductase, fdxD and fprD.