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 Polyangium aurulentum sp. SDU3-1 was found to produce the [delta]9,10 isomer (1) 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.