Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
J Mol Biol. 2010 Sep 24;402(3):539-51. doi: 10.1016/j.jmb.2010.07.053. Epub 2010 Aug 3.
PecS is a member of the MarR (multiple antibiotic resistance regulator) family, which has been shown in Erwinia to regulate the expression of virulence genes. MarR homologs typically bind a small molecule ligand, resulting in attenuated DNA binding. For PecS, the natural ligand has not been identified. We have previously shown that urate is a ligand for the Deinococcus radiodurans-encoded MarR homolog HucR (hypothetical uricase regulator) and identified residues responsible for ligand binding. We show here that all four residues involved in urate binding and propagation of conformational changes to DNA recognition helices are conserved in PecS homologs, suggesting that urate is the ligand for PecS. Consistent with this prediction, Agrobacterium tumefaciens PecS specifically binds urate, and urate attenuates DNA binding in vitro. PecS binds two operator sites in the intergenic region between the divergent pecS gene and pecM genes, one of which features two partially overlapping repeats to which PecS binds as a dimer on opposite faces of the duplex. Notably, urate dissociates PecS from cognate DNA, allowing transcription of both genes in vivo. Taken together, our data show that urate is a ligand for PecS and suggest that urate serves a novel function in signaling the colonization of a host plant.
PecS 是 MarR（多种抗生素耐药调节剂）家族的成员，已在欧文氏菌中表明其调节毒力基因的表达。MarR 同源物通常结合小分子配体，导致 DNA 结合减弱。对于 PecS，尚未确定其天然配体。我们之前曾表明尿酸是 Deinococcus radiodurans 编码的 MarR 同源物 HucR（假设尿酸酶调节剂）的配体，并确定了负责配体结合的残基。我们在这里表明，与尿酸结合和将构象变化传播到 DNA 识别螺旋有关的所有四个残基在 PecS 同源物中保守，表明尿酸是 PecS 的配体。与这一预测一致，根癌农杆菌 PecS 特异性结合尿酸，尿酸在体外减弱 DNA 结合。PecS 结合在发散的 pecS 基因和 pecM 基因之间的基因间区域的两个操纵子位点，其中一个具有两个部分重叠的重复序列，PecS 作为二聚体结合在双链体的相对面上。值得注意的是，尿酸使 PecS 从同源 DNA 上解离，从而允许两个基因在体内转录。总之，我们的数据表明尿酸是 PecS 的配体，并表明尿酸在信号宿主植物定植方面具有新的功能。
