Identification and Characterization of Bifunctional Drimenol Synthases of Marine Bacterial Origin

Natural drimane-type sesquiterpenes, including drimenol, display diversebiological activities. These active compounds are distributed in plants and fungi; however,their accumulation in bacteria remains unknown. Consequently, bacterial drimane-typesesquiterpene synthases remain to be characterized. Here, we reportfive drimenolsynthases (DMSs) of marine bacterial origin, all belonging to the haloacid dehalogenase(HAD)-like hydrolase superfamily with the conserved DDxxE motif typical of class Iterpene synthases and the DxDTT motif found in class II diterpene synthases. Theycatalyze two continuous reactions: the cyclization of farnesyl pyrophosphate (FPP) intodrimenyl pyrophosphate and dephosphorylation of drimenyl pyrophosphate intodrimenol. Protein structure modeling of the characterizedAquimarina spongiaeDMS(AsDMS) suggests that the FPP substrate is located within the interdomain created by theDDxxE motif of N-domain and DxDTT motif of C-domain. Biochemical analysis revealedtwo aspartate residues of the DDxxE motif that might contribute to the capture of thepyrophosphate moiety of FPP inside the catalytic site of AsDMS, which is essential for efficient cyclization and subsequentdephosphorylation reactions. The middle aspartate residue of the DxDTT motif is also critical for cyclization. Thus, AsDMS utilizesboth motifs in the reactions. Remarkably, the unique protein architecture of AsDMS, which is characterized by the fusion of a HAD-like domain (N-domain) and a terpene synthase beta domain (C-domain), significantly differentiates this new enzyme. Ourfindings ofthefirst examples of bacterial DMSs suggest the biosynthesis of drimane sesquiterpenes in bacteria and shed light on the divergenceof the structures and functions of terpene synthases.

Automated summary

This study reports five drimenol synthases (DMSs) from marine bacteria and reveals the biosynthesis of drimane sesquiterpenes in bacteria. Protein structure modeling and biochemical analysis shed light on the catalytic mechanism of AsDMS and further elucidate the diversity of structure and function of terpene synthases.