RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
J Bacteriol. 2011 Sep;193(17):4388-95. doi: 10.1128/JB.05203-11. Epub 2011 Jul 1.
Phenylacetic acid (PAA) is a common intermediate in the catabolic pathways of several structurally related aromatic compounds. It is converted into phenylacetyl coenzyme A (PA-CoA), which is degraded to general metabolites by a set of enzymes. Within the genome of the extremely thermophilic bacterium Thermus thermophilus HB8, a cluster of genes, including a TetR family transcriptional regulator, may be involved in PAA degradation. The gene product, which we named T. thermophilus PaaR, negatively regulated the expression of the two operons composing the gene cluster in vitro. T. thermophilus PaaR repressed the target gene expression by binding pseudopalindromic sequences, with a consensus sequence of 5'-CNAACGNNCGTTNG-3', surrounding the promoters. PA-CoA is a ligand of PaaR, with a proposed binding stoichiometry of 1:1 protein monomer, and was effective for transcriptional derepression. Thus, PaaR is a functional homolog of PaaX, a GntR transcriptional repressor found in Escherichia coli and Pseudomonas strains. A three-dimensional structure of T. thermophilus PaaR was predicted by homology modeling. In the putative structure, PaaR adopts the typical three-dimensional structure of the TetR family proteins, with 10 α-helices. A positively charged surface at the center of the molecule is similar to the acyl-CoA-binding site of another TetR family transcriptional regulator, T. thermophilus FadR, which is involved in fatty acid degradation. The CoA moiety of PA-CoA may bind to the center of the PaaR molecule, in a manner similar to the binding of the CoA moiety of acyl-CoA to FadR.
苯乙酸（PAA）是几种结构相关芳香族化合物分解代谢途径中的常见中间产物。它被转化为苯乙酰辅酶 A（PA-CoA），然后通过一系列酶将其降解为一般代谢物。在极端嗜热细菌 Thermus thermophilus HB8 的基因组中，有一组基因，包括一个 TetR 家族转录调节因子，可能参与 PAA 降解。该基因的产物，我们将其命名为 T. thermophilus PaaR，在体外负调控组成基因簇的两个操纵子的表达。T. thermophilus PaaR 通过结合围绕启动子的假回文序列来抑制靶基因的表达，其保守序列为 5'-CNAACGNNCGTTNG-3'。PA-CoA 是 PaaR 的配体，其结合比为 1:1 蛋白质单体，并且对转录去阻遏有效。因此，PaaR 是在大肠杆菌和假单胞菌中发现的 GntR 转录阻遏物 PaaX 的功能同源物。通过同源建模预测了 T. thermophilus PaaR 的三维结构。在假定的结构中，PaaR 采用了 TetR 家族蛋白的典型三维结构，具有 10 个α-螺旋。分子中心带正电荷的表面类似于另一个 TetR 家族转录调节因子 T. thermophilus FadR 的酰基辅酶 A 结合位点，该因子参与脂肪酸降解。PA-CoA 的 CoA 部分可能以类似于酰基辅酶 A 的 CoA 部分与 FadR 结合的方式结合到 PaaR 分子的中心。
