Binds 3 Mg(2+) ions per subunit. The Asp-Asp-Xaa-Xaa-Asp (DDXXD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Although similar to (1R,4R,5S)-(-)-guaia-6,10(14)-diene synthase, lacks the metal binding site Asn at position 288 and does not show (1R,4R,5S)-(-)-guaia-6,10(14)-diene synthase activity. Converting Lys-288 to a asparagine restores activity.