Catalyzes the formation of the 5-9-5 ring skeleton (3S,6S,11R,14S)-tsukubadiene from geranylgeranyl diphosphate (GGPP) via a 1,11-cyclization and a 10Re,14Re-cyclization. (2E,6E,10E)-geranylgeranyl diphosphate = diphosphate + tsukubadiene Binds 3 Mg(2+) ions per subunit. The Asp-Asp-Xaa-Xaa-Xaa-Glu (DDXXXE) and Ser-Xaa-Xaa-Xaa-Ser-Xaa-Xaa-Xaa-Glu (SSE) motifs are important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.