The Treponema pallidum tro operon encodes a multiple metal transporter, a zinc-dependent transcriptional repressor, and a semi-autonomously expressed phosphoglycerate mutase
The Treponema pallidum tro operon encodes a multiple metal transporter, a zinc-dependent transcriptional repressor, and a semi-autonomously expressed phosphoglycerate mutase
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DOI：
10.1074/jbc.m300781200
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发表时间：
2003-06-06
影响因子：
4.8
通讯作者：
Radolf, JD
中科院分区：
文献类型：
--
作者：
Hazlett, KRO;Rusnak, F;Radolf, JD
梅毒螺旋体的操纵子编码ABC转运蛋白（TroABCD）、转录抑制因子（TroR）和必需的糖酵解酶磷酸甘油酸变异酶（Gpm）。溶质结合蛋白（TroA）与Zn2+结合，而TroR在体外的DNA结合依赖于Mn2+，这一明显不一致的观察结果产生了渗透酶的配体和共抑制物身份的不确定性。此外，这种操纵子结构表明，在tror介导的抑制过程中，Gpm的表达和糖酵解（细菌ATP的唯一来源）将被暂停。为了解决这些差异，我们设计了一种实验策略，允许更直接地评估Tro操纵子的功能和调控。我们报道(i)载子- troa对Zn2+和Mn2+具有相同的亲和力；（ii）大肠杆菌中表达的Tro转运体进口Zn2+、Mn2+，可能还有铁；（iii）当Zn2+浓度显著低于Mn2+浓度时，TroR可抑制大肠杆菌中转运蛋白的表达；（iv）与gpm相比，tror介导的抑制导致转运蛋白基因的不成比例的下调。人体体液中Zn2+的浓度远高于Mn2+，这表明Zn2+是体内渗透酶的主要底物和共同抑制物。我们的数据还表明，当T. pallidum遇到高Zn2+水平时，Gpm的表达和糖酵解不会被取消。
The Treponema pallidum tro operon encodes an ABC transporter (TroABCD), a transcriptional repressor (TroR), and the essential glycolytic enzyme phosphoglycerate mutase (Gpm). The apparently discordant observations that the solute binding protein (TroA) binds Zn2+, whereas DNA binding by TroR in vitro is Mn2+-dependent, have generated uncertainty regarding the identities of the ligand(s) and co-repressor(s) of the permease. Moreover, this operonic structure suggests that Gpm expression, and hence glycolysis, the sole source of ATP for the bacterium, would be suspended during TroR-mediated repression. To resolve these discrepancies, we devised an experimental strategy permitting a more direct assessment of Tro operon function and regulation. We report that (i) apo-TroA has identical affinities for Zn2+ and Mn2+; (ii) the Tro transporter expressed in Escherichia coli imports Zn2+, Mn2+, and possibly iron; (iii) TroR represses transporter expression in E. coli at significantly lower concentrations of Zn2+ than of Mn2+; and (iv) TroR-mediated repression causes a disproportionately greater down-regulation of the transporter genes than of gpm. The much higher concentrations of Zn2+ than of Mn2+ in human body fluids suggests that Zn2+ is both the primary substrate and co-repressor of the permease in vivo. Our data also indicate that Gpm expression and, therefore, glycolysis would not be abrogated when T. pallidum encounters high Zn2+ levels.