A Single Residue Switch Controls Isomer Selectivity in the Myxobacterial Isobonnadiene Synthase

Myxobacterial terpenoids are rare and only a few myxobacterial terpene synthases are known. A terpene synthase, IbdS, from <i>Polyangium aurulentum</i> sp. SDU3-1 was found to produce the Δ^9,10 isomer (<b>1</b>) of the spirocyclic 6/7/5-tricyclic bonnadiene, along with several 6/10-eunicellanes and cembrenoids as minor products. Sequence comparison and site-directed mutagenesis of IbdS and the actinobacterial bonnadiene synthase revealed a single residue switch at position 57 controlling isomer selectivity.