The major pigment produced by Staphylococcus aureus Newman is the deep-yellow carotenoid 4,4'-diaponeurosporene; after prolonged cultivation, this pigment is in part converted to the orange end product staphyloxanthin. From this strain a 3.5-kb DNA fragment was identified which after being cloned into Escherichia coli and Staphylococcus carnosus conferred the ability to produce 4,4'-diaponeurosporene. DNA sequencing of this fragment revealed two open reading frames (ORFs) which are very likely cotranscribed. ORF1 encodes a 254-amino-acid hydrophobic protein, CrtM (M(r), 30,121). The deduced sequence of CrtM exhibits in three domains similarities to the sequences of Saccharomyces cerevisiae and human squalene synthases and phytoene synthases of various bacteria. ORF2 encodes a 448-amino-acid hydrophobic protein, CrtN, with an M(r) of 50,853 whose deduced sequence is similar to those of phytoene desaturases of other bacteria. At the N terminus of CrtN a classical FAD-, NAD(P)-binding domain is found. Spectrophotometry and gas chromatography-mass spectrometry analyses of the carotenoid production of E. coli and S. carnosus clones containing either ORF1 or both ORFs together suggest that ORF1 and ORF2 represent the dehydrosqualene synthase gene (crtM) and the dehydrosqualene desaturase gene (crtN), respectively. The results furthermore suggest that the biosynthesis of 4,4'-diaponeurosporene starts with the condensation of two molecules of farnesyl diphosphate by dehydrosqualene synthase (CrtM); it is shown that the reaction product of this enzyme is dehydrosqualene and not squalene. Dehydrosqualene (4,4'-diapophytoene) is successively dehydrogenated by a desaturase (CrtN) to form the yellow main intermediate 4,4'-diaponeurosporene.
金黄色葡萄球菌Newman产生的主要色素是深黄色的类
胡萝卜素4,4'-diaponeurosporene;在长时间培养后,这种色素部分转化为橙色的终产物staphyloxanthin。从该菌株中鉴定出一个3.5 kb的DNA片段,将其克隆到大肠杆菌和肉毒桿菌中后,赋予了产生4,4'-diaponeurosporene的能力。对该片段的DNA序列分析发现了两个开放阅读框(ORFs),这两个ORFs很有可能是共同转录的。ORF1编码一个254
氨基酸的疏
水性蛋白质CrtM(M(r),30,121)。CrtM的推导序列在三个领域与酿酒酵母和人类
角鲨烷合酶以及各种细菌的类
胡萝卜素合酶的序列相似。ORF2编码一个448
氨基酸的疏
水性蛋白质CrtN,其M(r)为50,853,其推导序列与其他细菌的类
胡萝卜素脱氢酶的序列相似。在CrtN的N端发现了一个经典的FAD-,
NAD(P)-结合域。大肠杆菌和肉毒桿菌的克隆体中包含ORF1或两个ORFs,经分光光度计和气相色谱质谱分析表明,ORF1和ORF2分别代表脱
水角鲨烷合酶
基因(crtM)和脱
水角鲨烷脱饱和酶
基因(crtN)。结果进一步表明,4,4'-diaponeurosporene的
生物合成始于2个双萜
磷酸分子的脱
水角鲨烷合酶(CrtM)的缩合;表明该酶的反应产物是脱
水角鲨烷而不是
角鲨烷。脱
水角鲨烷(4,4'-diapophytoene)被脱饱和酶(CrtN)连续脱氢,形成黄色的主要中间体4,4'-diaponeurosporene。