Milani Mario, Leoni Livia, Rampioni Giordano, Zennaro Elisabetta, Ascenzi Paolo, Bolognesi Martino
Giannina Gaslini Institute and INFM, Largo G. Gaslini 5, I-16147 Genova, Italy.
Structure. 2005 Sep;13(9):1289-97. doi: 10.1016/j.str.2005.05.014.
StyR belongs to the FixJ subfamily of signal transduction response regulators; it controls transcription of the styABCD operon coding for styrene catabolism in Pseudomonas fluorescens ST. The crystal structure of unphosphorylated StyR is reported at 2.2 A resolution. StyR is composed of an N-terminal regulatory domain (StyR-N) and a C-terminal DNA binding domain (StyR-C). The two domains are separated by an elongated linker alpha helix (34 residues), a new feature in known response regulator structures. StyR-C is structured similarly to the DNA binding domain of the response regulator NarL. StyR-N shows structural reorganization of the phosphate receiving region involved in activation/homodimerization: specific residues adopt an "active-like" conformation, and the alpha4 helix, involved in dimerization of the homologous FixJ response regulator, is trimmed to just one helical turn. Overall, structural considerations suggest that phosphorylation may act as an allosteric switch, shifting a preexisting StyR equilibrium toward the active, dimeric, DNA binding form.
StyR属于信号转导应答调节因子的FixJ亚家族；它控制着荧光假单胞菌ST中编码苯乙烯分解代谢的styABCD操纵子的转录。未磷酸化的StyR的晶体结构以2.2埃的分辨率报道。StyR由一个N端调节结构域（StyR-N）和一个C端DNA结合结构域（StyR-C）组成。这两个结构域由一个细长的连接α螺旋（34个残基）隔开，这是已知应答调节因子结构中的一个新特征。StyR-C的结构与应答调节因子NarL的DNA结合结构域相似。StyR-N显示了参与激活/同源二聚化的磷酸接收区域的结构重组：特定残基采用“活性样”构象，参与同源FixJ应答调节因子二聚化的α4螺旋被修剪成仅一圈螺旋。总体而言，结构方面的考虑表明，磷酸化可能充当变构开关，将预先存在的StyR平衡转向活性、二聚体、DNA结合形式。
