Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR47UH, UK.
Mol Microbiol. 2011 Oct;82(1):222-35. doi: 10.1111/j.1365-2958.2011.07812.x. Epub 2011 Sep 8.
The Per-ARNT-Sim (PAS) domain is a conserved α/β fold present within a plethora of signalling proteins from all kingdoms of life. PAS domains are often dimeric and act as versatile sensory and interaction modules to propagate environmental signals to effector domains. The NifL regulatory protein from Azotobacter vinelandii senses the oxygen status of the cell via an FAD cofactor accommodated within the first of two amino-terminal tandem PAS domains, termed PAS1 and PAS2. The redox signal perceived at PAS1 is relayed to PAS2 resulting in conformational reorganization of NifL and consequent inhibition of NifA activity. We have identified mutations in the cofactor-binding cavity of PAS1 that prevent 'release' of the inhibitory signal upon oxidation of FAD. Substitutions of conserved β-sheet residues on the distal surface of the FAD-binding cavity trap PAS1 in the inhibitory signalling state, irrespective of the redox state of the FAD group. In contrast, substitutions within the flanking A'α-helix that comprises part of the dimerization interface of PAS1 prevent transmission of the inhibitory signal. Taken together, these results suggest an inter-subunit pathway for redox signal transmission from PAS1 that propagates from core to the surface in a conformation-dependent manner requiring a flexible dimer interface.
过氧物酶-芳香烃受体核转录因子（PAS）结构域是一种保守的α/β折叠结构，存在于所有生命领域的大量信号蛋白中。PAS 结构域通常是二聚体，作为多功能的感觉和相互作用模块，将环境信号传递到效应结构域。固氮螺菌（Azotobacter vinelandii）的 NifL 调节蛋白通过容纳在两个氨基末端串联 PAS 结构域（称为 PAS1 和 PAS2）中的第一个的黄素腺嘌呤二核苷酸（FAD）辅因子来感知细胞的氧状态。在 PAS1 处感知到的氧化还原信号被传递到 PAS2，导致 NifL 的构象重排，从而抑制 NifA 活性。我们已经在 PAS1 的辅因子结合腔中鉴定出突变，这些突变阻止了 FAD 氧化时抑制信号的“释放”。FAD 结合腔远端表面上保守的β-折叠残基的取代将 PAS1 困在抑制信号状态中，而与 FAD 基团的氧化还原状态无关。相比之下，包含 PAS1 二聚化界面部分的侧翼 A'α-螺旋内的取代阻止了抑制信号的传递。总之，这些结果表明，从 PAS1 到表面的氧化还原信号传递存在一个亚基间途径，该途径以构象依赖的方式从核心传播，需要一个灵活的二聚体界面。
