A non-synonymous nucleotide substitution can account for one evolutionary route to sesquiterpene synthase activity in the TPS-b subgroup

Plant sesquiterpene and hemiterpene synthases in the monoterpene synthase dominated TPS-b subgroup are thought to have evolved independently from a monoterpene synthase ancestor. A TPS-b sesquiterpene synthase from apple (MdAFS1), which predominantly produces alpha-farnesene, can also synthesize the monoterpene (E)-beta-ocimene. The dual activity offered a functional link to an ancestral MdAFS1 enzyme and a rational basis for investigation of the evolution of TPS-b sesquiterpene enzymes. Protein modelling and mutagenesis analysis of the MdAFS1 active site identified a nonsynonymous nucleotide substitution that could account for the requisite shift in substrate specificity necessary for the emergence of its sesquiterpene activity during the evolution of the TPS-b enzymes. (C) 2011 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.