Journal Article

Characterization of Cyanobacterial Carotenoid Ketolase CrtW and Hydroxylase CrtR by Complementation Analysis in <i>Escherichia coli</i>

Takuya Makino, Hisashi Harada, Hiroshi Ikenaga, Satoru Matsuda, Shinichi Takaichi, Kazutoshi Shindo, Gerhard Sandmann, Takehiko Ogata and Norihiko Misawa

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 49, issue 12, pages 1867-1878
Published in print December 2008 | ISSN: 0032-0781
Published online December 2008 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcn169
Characterization of Cyanobacterial Carotenoid Ketolase CrtW and Hydroxylase CrtR by Complementation Analysis in Escherichia coli

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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

Journal Article.  5534 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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