Terpene cyclase that catalyzes the cyclization of farnesyl diphosphate (FPP) to delta(6)-protoilludene (PubMed:24166732, PubMed:26239156). In presence of Ca(2+), a significant switch from 1,11 to a dual 1,11/1,10 cyclization occurs, producing beta-elemene as the major product, with lower levels of delta(6)-protoilludene and (E)-beta-caryophyllene, and traces of beta-selinene and alpha-selinene (PubMed:26239156). (2E,6E)-farnesyl diphosphate = Delta(6)-protoilludene + diphosphate (2E,6E)-farnesyl diphosphate = alpha-selinene + diphosphate Mg(2+) and Mn(2+) are more tightly associated with the active site motifs (D(D/E)XX(D/E) and NSE) and thus lead to more efficient removal of PPi. Ca(2+) switches the cyclization mechanism of delta(6)-protoilludene synthase from 1,11 to 1,10 cyclization which leads to the production of beta-elemene. The 2 conserved active-site motifs D(D/E)XX(D/E) and NSE are required for coordinating the divalent metal ions that stabilize the PPi moiety of the substrate. Belongs to the terpene synthase family.