Sesquiterpene cyclase; part of the gene cluster that mediates the biosynthesis of heptelidic acid (HA), a sesquiterpene lactone that acts as an inhibitor of glyceraldehyde-3-phosphatedehydrogenase (GAPDH) and a growth inhibitor of the salt-tolerant lactic acid bacteria in soy sauce brewing. Binds 3 Mg(2+) ions per subunit. The expression is positively regulated by the 2 cluster-specific transcription factors hepR and hepS. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Abolishes the production of heptelidic acid. Belongs to the terpene synthase family.