Hanzelka B L, Greenberg E P
Department of Microbiology, University of Iowa, Iowa City 52242, USA.
J Bacteriol. 1996 Sep;178(17):5291-4. doi: 10.1128/jb.178.17.5291-5294.1996.
Synthesis of the autoinducer signal involved in the cell density-dependent activation of Vibrio fischeri luminescence is directed by luxI. The autoinducer is N-(3-oxohexanoyl)homoserine lactone, and little is known about its synthesis. We have measured autoinducer synthesis by amino acid auxotrophs of Escherichia coli that contained luxI on a high-copy-number plasmid. Experiments with cell suspensions starved for methionine or homoserine show that either methionine or S-adenosylmethionine but not homoserine or homoserine lactone is required for autoinducer synthesis. The S-adenosylmethionine synthesis inhibitor cycloleucine blocks methionine-dependent autoinducer synthesis. Thus, it appears that S-adenosylmethionine rather than methionine is the molecule required for autoinducer synthesis. The amount of 15N-labeled methionine incorporated into the autoinducer by growing cultures of a homoserine and a methionine auxotroph was measured by mass spectrometry. The labeling studies show that even in the presence of homoserine, almost all of the autoinducer produced contains the 15N label from methionine. Thus, it appears that S-adenosylmethionine serves as the amino acid substrate in the luxI-dependent synthesis of the V. fischeri autoinducer.
费氏弧菌发光的细胞密度依赖性激活所涉及的自诱导信号的合成由luxI指导。自诱导剂是N-(3-氧代己酰基)高丝氨酸内酯，对其合成了解甚少。我们通过在高拷贝数质粒上携带luxI的大肠杆菌氨基酸营养缺陷型来测量自诱导剂的合成。对缺乏蛋氨酸或高丝氨酸的细胞悬液进行的实验表明，自诱导剂合成需要蛋氨酸或S-腺苷甲硫氨酸，但不需要高丝氨酸或高丝氨酸内酯。S-腺苷甲硫氨酸合成抑制剂环亮氨酸可阻断蛋氨酸依赖性自诱导剂的合成。因此，似乎S-腺苷甲硫氨酸而非蛋氨酸是自诱导剂合成所需的分子。通过质谱法测量了高丝氨酸和蛋氨酸营养缺陷型生长培养物将15N标记的蛋氨酸掺入自诱导剂中的量。标记研究表明，即使存在高丝氨酸，几乎所有产生的自诱导剂都含有来自蛋氨酸的15N标记。因此，似乎S-腺苷甲硫氨酸在费氏弧菌自诱导剂的luxI依赖性合成中作为氨基酸底物。
