Graham Joel E, Bryant Donald A
Department of Biochemistry and Molecular Biology, S-235 Frear Building, The Pennsylvania State University, University Park, PA 16802, USA.
J Bacteriol. 2009 May;191(10):3292-300. doi: 10.1128/JB.00050-09. Epub 2009 Mar 20.
Synechococcus sp. strain PCC 7002 produces a variety of carotenoids, which comprise predominantly dicylic beta-carotene and two dicyclic xanthophylls, zeaxanthin and synechoxanthin. However, this cyanobacterium also produces a monocyclic myxoxanthophyll, which was identified as myxol-2' fucoside. Compared to the carotenoid glycosides produced by diverse microorganisms, cyanobacterial myxoxanthophyll and closely related compounds are unusual because they are glycosylated on the 2'-OH rather than on the 1'-OH position of the psi end of the molecule. In this study, the genes encoding two enzymes that modify the psi end of myxoxanthophyll in Synechococcus sp. strain PCC 7002 were identified. Mutational and biochemical studies showed that open reading frame SynPCC7002_A2032, renamed cruF, encodes a 1',2'-hydroxylase [corrected] and that open reading frame SynPCC7002_A2031, renamed cruG, encodes a 2'-O-glycosyltransferase. The enzymatic activity of CruF was verified by chemical characterization of the carotenoid products synthesized when cruF was expressed in a lycopene-producing strain of Escherichia coli. Database searches showed that homologs of cruF and cruG occur in the genomes of all sequenced cyanobacterial strains that are known to produce myxol or the acylic xanthophyll oscillaxanthin. The genomes of many other bacteria that produce hydroxylated carotenoids but do not contain crtC homologs also contain cruF orthologs. Based upon observable intermediates, a complete biosynthetic pathway for myxoxanthophyll is proposed. This study expands the suite of enzymes available for metabolic engineering of carotenoid biosynthetic pathways for biotechnological applications.
聚球藻属菌株PCC 7002能产生多种类胡萝卜素，主要包括双环β-胡萝卜素以及两种双环叶黄素，即玉米黄质和集球藻黄素。然而，这种蓝细菌还能产生一种单环的粘杆藻黄素，经鉴定为粘醇-2'-岩藻糖苷。与多种微生物产生的类胡萝卜素糖苷相比，蓝细菌的粘杆藻黄素及与之密切相关的化合物较为特殊，因为它们是在分子ψ端的2'-OH而非1'-OH位置进行糖基化。在本研究中，鉴定出了聚球藻属菌株PCC 7002中编码两种修饰粘杆藻黄素ψ端的酶的基因。突变和生化研究表明，开放阅读框SynPCC7002_A2032（重新命名为cruF）编码一种1',2'-羟化酶[已修正]，开放阅读框SynPCC7002_A2031（重新命名为cruG）编码一种2'-O-糖基转移酶。当cruF在产番茄红素的大肠杆菌菌株中表达时，通过对合成的类胡萝卜素产物进行化学表征，验证了CruF的酶活性。数据库搜索显示，cruF和cruG的同源物存在于所有已知能产生粘醇或无环叶黄素振荡黄质的已测序蓝细菌菌株的基因组中。许多其他产生羟基化类胡萝卜素但不含crtC同源物的细菌基因组中也含有cruF直系同源物。基于可观察到的中间产物，提出了一条完整的粘杆藻黄素生物合成途径。本研究扩展了可用于类胡萝卜素生物合成途径代谢工程以进行生物技术应用的酶的种类。
