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Plant and Cell Physiology Advance Access originally published online on November 5, 2008
Plant and Cell Physiology 2008 49(12):1867-1878; doi:10.1093/pcp/pcn169
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Characterization of Cyanobacterial Carotenoid Ketolase CrtW and Hydroxylase CrtR by Complementation Analysis in Escherichia coli

Takuya Makino1, Hisashi Harada2,6, Hiroshi Ikenaga2, Satoru Matsuda2, Shinichi Takaichi3, Kazutoshi Shindo4, Gerhard Sandmann5, Takehiko Ogata1 and Norihiko Misawa2,6,*

1School of Fisheries Sciences, Kitasato University, Sanriku-cho, Ofunato, 022-0101 Japan
2Marine Biotechnology Institute, Heita, Kamaishi, 026-0001 Japan
3Department of Biology, Nippon Medical School, Nakahara, Kawasaki, 211-0063 Japan
4Japan Women's University, Bunkyo-ku, Tokyo, 112-8681 Japan
5Molecular Biosciences 213, J. W. Goethe University, D-60054 Frankfurt/M, Germany

*Corresponding author: E-mail, n-misawa{at}ishikawa-pu.ac.jp; Fax, + 81-76-227-7557.


  Abstract

The pathway from β-carotene to astaxanthin is a crucial step in the synthesis of astaxanthin, a red antioxidative ketocarotenoid that confers beneficial effects on human health. Two enzymes, a β-carotene ketolase (carotenoid 4,4'-oxygenase) and a β-carotene hydroxylase (carotenoid 3,3'-hydroxylase), are involved in this pathway. Cyanobacteria are known to utilize the carotenoid ketolase CrtW and/or CrtO, and the carotenoid hydroxylase CrtR. Here, we compared the catalytic functions of CrtW ketolases, which originated from Gloeobacter violaceus PCC 7421, Anabaena (also known as Nostoc) sp. PCC 7120 and Nostoc punctiforme PCC 73102, and CrtR from Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120 and Anabaena variabilis ATCC 29413 by complementation analysis using recombinant Escherichia coli cells that synthesized various carotenoid substrates. The results demonstrated that the CrtW proteins derived from Anabaena sp. PCC 7120 as well as N. punctiforme PCC 73102 (CrtW148) can convert not only β-carotene but also zeaxanthin into their 4,4'-ketolated products, canthaxanthin and astaxanthin, respectively. In contrast, the Anabaena CrtR enzymes were very poor in accepting either β-carotene or canthaxanthin as substrates. By comparison, the Synechocystis sp. PCC 6803 CrtR converted β-carotene into zeaxanthin efficiently. We could assign the catalytic functions of the gene products involved in ketocarotenoid biosynthetic pathways in Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120 and N. punctiforme PCC 73102, based on the present and previous findings. This explains why these cyanobacteria cannot produce astaxanthin and why only Synechocystis sp. PCC 6803 can produce zeaxanthin.

Keywords: Anabaena sp. PCC 7120 - β-Carotene - Carotenoid - CrtR - CrtW - Nostoc punctiforme

Abbreviations: APCI-MS, atmospheric pressure chemical ionization mass spectrometer; PDA, photodiode array detection

6Present address: Central Laboratories for Frontier Technology, Kirin Holdings Co. Ltd., i-BIRD, Nonoichi-machi, Ishikawa, 921-8836 Japan.

(Received September 5, 2008; Accepted October 31, 2008)
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