Tolmasky M E, Actis L A, Crosa J H
Department of Microbiology and Immunology, School of Medicine, Oregon Health Sciences University, Portland 97201-3098.
Infect Immun. 1993 Aug;61(8):3228-33. doi: 10.1128/iai.61.8.3228-3233.1993.
The siderophore anguibactin is produced in vivo in a diffusible form and is an important factor in the virulence of Vibrio anguillarum. The natural isolate V. anguillarum 531A is a hyperproducer of anguibactin when compared with the prototype strain V. anguillarum 775. The angR gene was found to be responsible for this difference in levels of anguibactin produced. Nucleotide sequence analysis showed that the angR531A differed in a single nucleotide from the angR775 present in the prototype plasmid pJM1. This nucleotide substitution resulted in a change in amino acid 267 from His in strain 775 to Asn in strain 531A. This amino acid is located in a region between one of the two helix-turn-helix domains and the neighboring leucine zipper. Mutations to replace His with either Leu or Gln, generated by site-directed mutagenesis, in amino acid 267 resulted in strains for which the MIC of the iron chelator ethylenediamine di(o-hydroxyphenyl) acetic acid were lower than for the proptotype 775 but higher than for iron uptake-deficient strains. In addition to its transcriptional activating function, AngR also complemented a mutation in the Escherichia coli entE gene, which encodes the enterobactin biosynthetic enzyme 2,3-dihydroxybenzoate-AMP ligase. Therefore, AngR may also function in V. anguillarum as an EntE-like enzyme for the biosynthesis of anguibactin.
铁载体鳗弧菌素在体内以可扩散的形式产生，是鳗弧菌致病性的一个重要因素。与原型菌株鳗弧菌775相比，天然分离株鳗弧菌531A是鳗弧菌素的高产菌株。发现angR基因是造成鳗弧菌素产生水平差异的原因。核苷酸序列分析表明，angR531A与原型质粒pJM1中存在的angR775在一个核苷酸上不同。这种核苷酸替换导致第267位氨基酸从775菌株中的组氨酸变为531A菌株中的天冬酰胺。该氨基酸位于两个螺旋-转角-螺旋结构域之一与相邻亮氨酸拉链之间的区域。通过定点诱变将第267位氨基酸的组氨酸分别替换为亮氨酸或谷氨酰胺所产生的突变菌株，其铁螯合剂乙二胺二（邻羟基苯基）乙酸的最低抑菌浓度低于原型菌株775，但高于铁摄取缺陷型菌株。除了其转录激活功能外，AngR还弥补了大肠杆菌entE基因的突变，该基因编码肠杆菌素生物合成酶2,3-二羟基苯甲酸-AMP连接酶。因此，AngR在鳗弧菌中也可能作为一种类似于EntE的酶发挥作用，参与鳗弧菌素的生物合成。
