Enzymatic Plasticity Inspired by the Diterpene Cyclase CotB2.

Enzymatic plasticity, as a modern term referring to the functional conversion of an enzyme, is significant for enzymatic activity redesign. The bacterial diterpene cyclase CotB2 is a typical plastic enzyme by which its native form precisely conducts a chemical reaction while its mutants diversify the catalytic functions drastically. Many efforts have been made to disclose the mysteries of CotB2 enzyme catalysis. However, the catalytic details and regulatory mechanism toward the precise chemo- and stereoselectivity are still elusive. In this work, multiscale simulations are employed to illuminate the biocyclization mechanisms of the linear substrate into the final product cyclooctat-9-en-7-ol with a 5-8-5 fused ring scaffold, and the derailment products arising from the premature quenching of reactive carbocation intermediates are also discussed. The two major regulatory factors, local electrostatic stabilization effects from aromatic residues or polar residue in pocket and global features of active site including pocket-contour and pocket-hydrophobicity, are responsible for the enzymatic plasticity of CotB2. Further comparative studies of representative Euphorbiaceae and fungal diterpene cyclase (RcCS and PaFS) show a correlation between pocket plasticity and product diversity, which inspires a tentative enzyme product prediction and the rational diterpene cyclases' reengineering in the future.