Characterization of Two Chimeric Sesterterpene Synthases from a Fungal Symbiont Isolated from a Sesterterpenoid-Producing Lamiaceae Plant Leucosceptrum Canum

Two chimeric sesterterpene synthases（Aa TPS1 and Aa TPS2） were functionally characterized from Alternaria alternata MB-30 isolated from the leaves of a sesterterpenoid-producing Lamiaceae plant Leucosceptrum canum. Aa TPS1 generated a 5/8/6/5 tetracyclic sesteraltererol（1） and its absolute stereochemistry was determined by X-ray crystallographic analysis of its derivative 10,11-epoxysesteraltererol（2）, which enabled revision of the absolute configuration of C7 of sesterfisherol produced by Nf SS and PTTS014 characterized previously and its derivative 10,11-epoxysesterfisherol. Aa TPS2 produced a 5/15 bicyclic preterpestacin I（3）. Site-directed mutagenesis suggested that F192 in Aa TPS1 was likely involved in controlling of the hydroxylation of C12, and eight amino acids were important for the enzyme activity of Aa TPS1 and Aa TPS2. The engineered Escherichia coli and Saccharomyces cerevisiae strains were constructed for the productions of compounds 1 and 3, and the highest titer of compound 1 reached 62.3 mg/L in shake-flask culture. Both compounds 1 and 2 showed anti-adipogenic activity.