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Enzymatic Cascade Reactions for the Synthesis of Chiral Amino Alcohols from L-lysine
Published on: February 16, 2018
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Algal Kainoid Synthases Exhibit Substrate-Dependent Hydroxylation and Cyclization Activities
Austin R Hopiavuori1, Shaun M K McKinnie1
1Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California 95064, United States.
ACS Chemical Biology
|December 4, 2023
Summary
Microalgal DabC, a kainoid synthase, uniquely performs stereospecific hydroxylation, not C-C bond formation. This dual activity, conserved in related enzymes, offers insights into substrate recognition and biocatalysis.
Area of Science:
- Biochemistry
- Enzymology
- Organic Chemistry
Background:
- Fe(II)/α-ketoglutarate-dependent dioxygenases (Fe/αKG) are a large enzyme family known for C-H bond functionalization, typically via hydroxylation.
- Microalgal DabC was previously identified for its unique C-C bond formation in domoic acid biosynthesis, constructing a pyrrolidine ring.
Purpose of the Study:
- To investigate the catalytic activity of microalgal DabC and its homologues.
- To elucidate the substrate-dependent reactivity and mechanistic pathways of DabC.
- To explore the biocatalytic potential of kainoid synthases.
Main Methods:
- Enzyme kinetics and mechanistic studies using native and alternative substrates.
- Analysis of radical cyclization and β-hydroxylation pathways.
- Comparative analysis of conserved homologues (RadC1, KabC).
Main Results:
- Microalgal DabC exclusively performs stereospecific β-hydroxylation on its *cis* substrate regioisomer, contradicting its presumed C-C bond forming role.
- A 20-fold rate increase was observed for DabC radical cyclization over β-hydroxylation.
- No 1,5-hydrogen atom transfer was detected, indicating a distinct mechanism.
- This dual activity was conserved in macroalgal RadC1 and KabC homologues.
Conclusions:
- DabC's primary function is stereospecific hydroxylation, not C-C bond formation, challenging previous assumptions.
- Substrate recognition and reactivity trends in kainoid synthases are influenced by substrate-specific chemistry.
- Understanding this substrate-dependent reactivity enhances knowledge of kainoid synthases and their biocatalytic applications.
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