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Discovery and Biocatalytic Application of a PLP-Dependent Amino Acid γ-Substitution Enzyme that Catalyzes C-C Bond Formation

preprint
submitted on 31.03.2020 and posted on 01.04.2020 by Mengbin Chen, Chun-Ting Liu, Yi Tang
Pyridoxal phosphate (PLP)-dependent enzymes can catalyze various transformations of amino acids at alpha, beta, and gamma positions. These versatile enzymes are prominently involved in the biosynthesis of nonproteinogenic amino acids as building blocks of natural products, and are attractive biocatalysts. Here, we report the discovery of a two-step enzymatic synthesis of (2S, 6S)-6-methyl pipecolate 1, from the biosynthetic pathway of indole alkaloid citrinadin. The key enzyme CndF is PLP-dependent and catalyzes synthesis of (S)-2-amino-6-oxoheptanoate 3 that is in equilibrium with the cyclic Schiff base. The second enzyme CndE is a stereoselective imine reductase that gives 1. Biochemical characterization of CndF showed this enzyme performs gamma-elimination of O-acetyl L-homoserine to generate the vinylglycine ketimine, which is subjected to nucleophilic attack by acetoacetate to form the new Cgamma-Cdelta bond in 3 and complete the gamma-substitution reaction. CndF displays substrate promiscuity towards different beta-keto carboxylate and esters. Using a recombinant Aspergillus strain expressing CndF and CndE, feeding various alkyl-beta-keto esters led to the biosynthesis of 6-substituted L-pipecolates. The discovery of CndF expands the repertoire of reactions that can be catalyzed by PLP-dependent enzymes.

Funding

NIH 1R35GM118056

NSF CHE-1048804

History

Email Address of Submitting Author

mengbinchen@ucla.edu

Institution

University of California Los Angeles

Country

USA

ORCID For Submitting Author

0000-0001-6135-8661

Declaration of Conflict of Interest

No conflict of interst.

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