The green alga Chlorella zofingiensis produces large amounts of the valuable ketocarotenoid astaxanthin under dark, heterotrophic growth conditions, making it potentially employable for commercial production of astaxanthin as feed additives, colorants, and health products. Here, we report the identification and characterization of a β-carotene oxygenase (CRTO) gene that is directly involved in the biosynthesis of ketocarotenoids in C. zofingiensis. The open reading frame of the crtO gene, which is interrupted by three introns of 243, 318, and 351 bp, respectively, encodes a polypeptide of 312 amino acid residues. Only one crtO gene was detected in the genome of C. zofingiensis. Furthermore, the expression of the crtO gene was transiently up-regulated upon glucose treatment. Functional complementation in Escherichia coli showed that the coding protein of the crtO gene not only exhibits normal CRTO activity by converting β-carotene to canthaxanthin via echinenone, but also displays a high enzymatic activity of converting zeaxanthin to astaxanthin via adonixanthin. Based on the bifunctional CRTO, a predicted pathway for astaxanthin biosynthesis in C. zofingiensis is described, and the CRTO is termed as carotenoid 4,4′-β-ionone ring oxygenase.
Isolation and characterization of a carotenoid oxygenase gene from Chlorella zofingiensis (Chlorophyta)
Junchao Huang,Yan Wang,G. Sandmann,Feng Chen
Published 2006 in Applied Microbiology and Biotechnology
ABSTRACT
PUBLICATION RECORD
- Publication year
2006
- Venue
Applied Microbiology and Biotechnology
- Publication date
2006-07-01
- Fields of study
Biology, Medicine, Chemistry, Environmental Science
- Identifiers
- External record
- Source metadata
Semantic Scholar, PubMed
CITATION MAP
EXTRACTION MAP
CLAIMS
CONCEPTS
- adonixanthin
A carotenoid intermediate identified in the conversion of zeaxanthin toward astaxanthin.
- astaxanthin
A ketocarotenoid product of interest in Chlorella zofingiensis and the endpoint product assessed in the zeaxanthin conversion assay.
- canthaxanthin
A ketocarotenoid product formed from β-carotene in the enzyme assay system.
- chlorella zofingiensis
A green microalga examined here as the source of the carotenoid oxygenase gene and astaxanthin biosynthetic activity.
- crto gene
The carotenoid oxygenase gene isolated from Chlorella zofingiensis that encodes the CRTO protein.
Aliases: crtO
- echinenone
A carotenoid intermediate measured as a product of β-carotene oxidation in the assay system.
- glucose treatment
The experimental addition of glucose used to test how crtO expression responds under heterotrophic conditions.
Aliases: glucose
- zeaxanthin
A carotenoid substrate used to test the second activity of the CRTO protein.
- β-carotene
A carotenoid substrate used in the functional complementation assays for CRTO activity.
- β-carotene oxygenase (crto)
The carotenoid-cleaving enzyme encoded by crtO and discussed here as the protein product responsible for ketocarotenoid-related conversions.
Aliases: CRTO, carotenoid 4,4′-β-ionone ring oxygenase
REFERENCES
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