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Updated: Oct 18, 2025
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Structural Biology and Analytical Chemistry Approaches for Characterizing C-Glycoside Metabolic Enzymes in Human Gut Microbiota
Published on: May 23, 2025
646
FAD-dependent C-glycoside-metabolizing enzymes in microorganisms: Screening, characterization, and crystal structure
Takuto Kumano1,2, Sanae Hori1, Satomi Watanabe1
1Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
Summary
Researchers discovered a novel enzyme, C-glycoside 3-oxidase (CarA), that breaks down the natural C-glycoside carminic acid. This enzyme and its relatives are found in soil microbes, suggesting a key role in C-glycoside metabolism in nature.
Area of Science:
- Biochemistry
- Microbiology
- Enzymology
Background:
- C-glycosides possess a unique chemical structure with a direct carbon-to-carbon bond between the sugar and aglycone.
- Carminic acid, a natural C-glycoside, is widely used in food, cosmetic, and pharmaceutical industries, with global production exceeding 200 tons annually.
- The metabolic pathway for carminic acid has remained unidentified until this study.
Purpose of the Study:
- To identify microorganisms capable of catabolizing carminic acid.
- To discover and characterize the enzyme responsible for carminic acid degradation.
- To elucidate the biochemical mechanisms and structural basis of C-glycoside metabolism.
Main Methods:
- Isolation and cultivation of a novel carminic acid-catabolizing microorganism.
- Cloning and heterologous expression of the identified flavoenzyme, C-glycoside 3-oxidase (CarA), and its homologs.
- Biochemical characterization of CarA and its homologs, including substrate specificity and catalytic activity.
- Determination of the crystal structure of a CarA homolog.
- Mutagenesis analysis to investigate enzyme mechanisms.
Main Results:
- A previously unknown microorganism capable of degrading carminic acid was isolated.
- A novel flavoenzyme, C-glycoside 3-oxidase (CarA), was discovered, catalyzing the oxidation of carminic acid's sugar moiety.
- BLAST searches revealed that CarA homologs are prevalent in soil microorganisms but absent in intestinal microbes.
- Biochemical and structural analyses elucidated the substrate specificity and catalytic mechanisms of CarA and its homologs.
- The study identified key enzymes involved in the natural metabolism of C-glycosides.
Conclusions:
- CarA is a novel flavoenzyme that initiates the catabolism of carminic acid.
- The distribution of CarA homologs suggests a significant role in the environmental metabolism of C-glycosides.
- Understanding the structure-function relationship of CarA provides insights into C-glycoside metabolism in microorganisms.
