Traveling two diverging roads cytochrome-P450 catalyzed demethylation and γ-lactone formation in bacterial gibberellin biosynthesis

摘要

Biosynthesis of the gibberellin plant hormones evolved independently in plants and microbes, but the pathways proceed via similar transformations. The combined demethylation and γ-lactone ring forming transformation is of significant mechanistic interest, yet remains opaque. The relevant CYP112 from bacteria was probed via activity assays and ¹⁸O2 labeling experiments. Notably, the ability of tert-butyl hydroperoxide to drive this transformation indicates use of the ferryl-oxo (Compound I) from the CYP catalytic cycle for this reaction. Together with the confirmed loss of C-20 as CO2, this necessitates two catalytic cycles for carbon-carbon bond scission and γ-lactone formation. The ability of CYP112 to hydroxylate the δ-lactone form of GA15 shown by the labeling studies is consistent with the implied use of a further oxygenated heterocycle in the final conversion of GA24 to GA9, with the partial labeling of GA9 demonstrating that CYP112 partitions its reactants between two diverging mechanisms.