Secondary environmental variation creates a shifting evolutionary watershed for the methyl-parathion hydrolase enzyme

Enzymes can evolve new catalytic activity when their environments change to present them with novel substrates. Despite this seemingly straightforward relationship, factors other than the direct catalytic target can also impact enzyme adaptation. Here, we characterize the adaptive landscape separating an ancestral dihydrocoumarin hydrolase from a methyl parathion hydrolase descendant under eight different environments supplemented with alternative divalent metals. This variation shifts an evolutionary watershed, causing the outcome of adaptation to depend on the environment in which it occurs. The resultant landscapes also vary in terms both the number and the genotype(s) of “fitness peaks” as a result of genotype-by-environment (G×E) interactions and environment-dependent epistasis (G×G×E). This suggests that adaptive landscapes may be fluid and that molecular adaptation is highly contingent not only on obvious factors (such as catalytic targets) but also on less obvious secondary environmental factors that can direct it toward distinct outcomes.