Insight into the mechanism of the ring contraction reaction in bacterial gibberellin biosynthesis

What is it about?

Plants, fungi, and bacteria can all produce gibberellins (GAs), which act as plant hormones. Interestingly, each of these kingdoms of life has derived a different set of enzymes and biosynthetic reactions to produce the final bioactive hormones. However, all three biosynthetic pathways proceed through an analogous cytochrome P450-catalyzed oxidative ring contraction reaction, which is the crucial step that defines the carbon backbone of GAs. The mechanism of this reaction has previously been studied in plant and fungal GA biosynthesis, and here we analyzed the reaction from the bacterial pathway by using isotope labeling substrates and NMR analysis. This work determined that the overall mechanism of this reaction is shared between plant, fungal, and bacterial biosynthesis.

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Why is it important?

Collectively, it is striking that plants, fungi, and bacteria have co-evolved independent GA biosynthetic pathways, particularly due to the complexity and number of reactions involved (>8 enzymes and >10 chemical transformations). However, the presence of a highly conserved reaction such as this ring contraction suggests that the convergent evolution of these biosynthetic pathways must have been under certain biophysical/biochemical constraints that limited the possible routes by which these organisms could synthesize the same molecule.