Enzymatic assembly of the salinosporamide gamma-lactam-beta- lactone anticancer warhead Katherine Bauman 1 , Vikram V. Shende 1 , Percival Yang-Ting Chen 1,2 , Daniela B. B. Trivella 1,3,4 , Tobias A. M. Gulder 1,5 , Sreekumar Vellalath 6 , Daniel Romo 6 , Bradley S. Moore 1,7 1 Scripps Institution of Oceanography, University of California San Diego, USA, 2 Morphic Therapeutics, Waltham, USA, 3 National Center for Research in Energy and Materials, Brazil, 4 University of Campinas, Brazil, 5 Technical University of Dresden, Germany 6 Baylor University, USA, 7 Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, USA The marine microbial natural product salinosporamide A (Marizomib) is a potent proteasome inhibitor currently in phase III clinical trials for the treatment of glioblastoma brain tumors. Salinosporamide A is characterized by a complex and densely functionalized γ-lactam-β-lactone bicyclic warhead, the assembly of which has long remained a biosynthetic mystery.While a tremendous amount of work has elucidated the metabolic building blocks of salinosporamide A, there is as of yet no precedent for the key biosynthetic step(s) to construct the pharmacophore itself. This talk will report on the discovery of anenzymatic route to the salinosporamide core catalyzed by a standalone ketosynthase, SalC. Chemoenzymatic synthesis of carrier protein-tethered substrates, as well as intact proteomics, allowed us to probe the reactivity of SalC and understand its role as an intramolecular aldolase/β-lactone synthase with roles in both transacylation and bond forming reactions. Additionally, this talk will discuss molecular insights gained fromthe 2.85 Å SalC crystal structure that, combined with site-directed mutagenesis, allowed us to propose a bicyclization reaction mechanism. Ultimately, this work challenges our current understanding of the role of ketosynthase enzymes,expands our understanding of the efficient assembly line construction of mature salinosporamide A, and establishes a basis for future efforts towards the streamlined chemoenzymatic production of a clinically relevant chemotherapeutic.
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© The Author(s), 2022
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