Structural diversity of isoprene synthases in mosses from multiple terpenoid synthase lineages

Isoprene, a C5 hydrocarbon emitted by various land plants, serves as a protective molecule under heat stress. The moss Calohypnum plumiforme isoprene synthase (CpISPS) catalyzes isoprene formation from dimethylallyl diphosphate and contains two aromatic residues (Y393 and F615) at the bottom of the active site that restrict the cavity size to accommodate the smaller C5 substrate. Here we show that these residues are critical determinants of substrate size selectivity. Substitution of the two res