Choi Seon-Kang, Harada Hisashi, Matsuda Satoru, Misawa Norihiko
Marine Biotechnology Institute, Heita, Kamaishi-shi, Iwate 026-0001, Japan.
Appl Microbiol Biotechnol. 2007 Jul;75(6):1335-41. doi: 10.1007/s00253-007-0967-z. Epub 2007 Apr 6.
The pathways from beta-carotene to astaxanthin are crucial key steps for producing astaxanthin, one of industrially useful carotenoids, in heterologous hosts. Two beta-carotene ketolases (beta-carotene 4,4'-oxygenase), CrtO and CrtW, with different structure are known up to the present. In this paper, we compared the catalytic functions of a CrtO ketolase that was obtained from a marine bacterium Rhodococcus erythropolis strain PR4, CrtO derived from cyanobacterium Synechosistis sp. PCC6803, and CrtW derived from a marine bacterium Brevundimonas sp. SD212, by complementation analysis in Escherichia coli expressing the known crt genes. Results strongly suggested that a CrtO-type ketolase was unable to synthesize astaxanthin from zeaxanthin, i.e., only a CrtW-type ketolase could accept 3-hydroxy-beta-ionone ring as the substrate. Their catalytic efficiency for synthesizing canthaxanthin from beta-carotene was also examined. The results obtained up to the present clearly suggest that the bacterial crtW and crtZ genes are a combination of the most promising gene candidates for developing recombinant hosts that produce astaxanthin as the predominant carotenoid.
从β-胡萝卜素到虾青素的途径是在异源宿主中生产虾青素（一种具有工业用途的类胡萝卜素）的关键步骤。目前已知两种结构不同的β-胡萝卜素酮醇酶（β-胡萝卜素4,4'-加氧酶），即CrtO和CrtW。在本文中，我们通过在表达已知crt基因的大肠杆菌中进行互补分析，比较了从海洋红球菌PR4菌株获得的CrtO酮醇酶、来自蓝藻集胞藻PCC6803的CrtO以及来自海洋短杆菌SD212的CrtW的催化功能。结果有力地表明，CrtO型酮醇酶无法从玉米黄质合成虾青素，即只有CrtW型酮醇酶能够接受3-羟基-β-紫罗兰酮环作为底物。还检测了它们从β-胡萝卜素合成角黄素的催化效率。目前获得的结果清楚地表明，细菌crtW和crtZ基因是开发以虾青素作为主要类胡萝卜素的重组宿主的最有前景的基因候选组合。
