Fungal 1,11 cyclizing sesquiterpene synthases are product specific under typical reaction conditions. However, in vivo expression of certain Δ6-protoilludene synthases results in dual 1,11 and 1,10 cyclization. To determine the factors regulating this mechanistic variation, in-depth in vitro characterization of Δ6-protoilludene synthases was conducted. Divalent metal ions determine cyclization specificity and this product variability. Promiscuity in metal binding is mediated by secondary metal-binding sites away from the conserved D(D/E)XX(D/E) motif in sesquiterpene synthases. Phylogenetic analysis revealed a divergent evolution of Basidiomycota trans-humulyl cation producing sesquiterpene synthases, results that indicate a wider diversity in function than previously predicted. This study provides key insights into the function and evolution of 1,11 cyclizing fungal sesquiterpene synthases.
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