Molecular basis defining human Chlamydia trachomatis tissue tropism -: A possible role for tryptophan synthase
Molecular basis defining human Chlamydia trachomatis tissue tropism -: A possible role for tryptophan synthase
复制标题
DOI：
10.1074/jbc.m203937200
复制
发表时间：
2002-07-26
影响因子：
4.8
通讯作者：
McClarty, G
中科院分区：
文献类型：
--
作者：
Fehlner-Gardiner, C;Roshick, C;McClarty, G
在这里，我们报告克隆和测序衣原体染色体的一个区域称为“可塑性区”，从所有的人类沙眼衣原体血清型含有色氨酸生物合成基因。我们的研究结果表明，该区域包含色氨酸抑制因子的同源物以及色氨酸合成酶的α和β亚基。逆转录pcr和Western blot分析结果表明，trpBA基因得到转录，蛋白产物得到表达。所有血清型的TrpB序列高度保守。与其他色氨酸合成酶β亚基相比，衣原体TrpB亚基保留了β反应活性所需的所有保守氨基酸残基。相比之下，衣原体的TrpA序列显示出许多突变，这将它们与所有其他原核生物的TrpA序列区分开来。所有眼血清型都含有缺失突变，导致TrpA蛋白截短，缺乏反应活性。来自生殖器血清型的TrpA蛋白保留了催化所需的保守氨基酸，但在参与底物结合的几个活性位点残基发生了突变。对大肠杆菌色氨酸生物合成突变菌株的互补分析，以及克隆的TrpB和TrpA蛋白的体外酶活性数据表明，这些突变导致TrpA蛋白无法利用吲哚甘油3-磷酸作为底物。相比之下，衣原体TrpB蛋白可以进行β反应，催化吲哚和丝氨酸生成色氨酸。衣原体TrpB蛋白的活性与大肠杆菌和沙门氏菌的TrpBs不同，它对全长TrpA有绝对的要求。综上所述，我们的数据表明，生殖器，而不是眼睛，血清型能够利用外源吲哚进行色氨酸的生物合成。
Here we report the cloning and sequencing of a region of the chlamydiae chromosome termed the "plasticity zone" from all the human serovars of C. trachomatis containing the tryptophan biosynthesis genes. Our results show that this region contains orthologues of the tryptophan repressor as well as the alpha and beta subunits of tryptophan synthase. Results from reverse transcription-PCR and Western blot analyses indicate that the trpBA genes are transcribed, and protein products are expressed. The TrpB sequences from all serovars are highly conserved. In comparison with other tryptophan synthase beta subunits, the chlamydial TrpB subunit retains all conserved amino acid residues required for beta reaction activity. In contrast, the chlamydial TrpA sequences display numerous mutations, which distinguish them from TrpA sequences of all other prokaryotes. All ocular serovars contain a deletion mutation resulting in a truncated TrpA protein, which lacks a reaction activity. The TrpA protein from the genital serovars retains conserved amino acids required for catalysis but has mutated several active site residues involved in substrate binding. Complementation analysis in Escherchia coli strains, with defined mutations in tryptophan biosynthesis, and in vitro enzyme activity data, with cloned TrpB and TrpA proteins, indicate these mutations result in a TrpA protein that is unable to utilize indole glycerol 3-phosphate as substrate. In contrast, the chlamydial TrpB protein can carry out the betareaction, which catalyzes the formation of tryptophan from indole and serine. The activity of the chlamydial Trp B protein differs from that of the well characterized E. coli and Salmonella TrpBs in displaying an absolute requirement for full-length TrpA. Taken together our data indicate that genital, but not ocular, serovars are capable of utilizing exogenous indole for the biosynthesis of tryptophan.