SIGNALING STATE OLIGOMERIZATION OF THE SLR1694 BLUF DOMAIN DURING PHOTOCYCLE

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 所有的生物都有能力对光、电压、氧、配体和环境因素等生物刺激做出反应。当施加刺激时，每个刺激在几个步骤中转化为特定的细胞反应，从而促进信号转导途径。要了解信号转导的工作机制，重要的是确定参与信号转导的分子单位，例如刺激受体。在这些刺激中，光在包括光合作用和基因表达在内的一系列具有重要生物学意义的细胞反应中发挥着重要作用。到目前为止，已经鉴定了六种光受体(2)。在这些光感受器中，BLUF结构域是最近发现的，因此对它的研究还很有限。特别是，Slr1694 BLUF结构域在溶液中以均二聚体形式存在，但在黑暗中齐聚形成十聚体。这种假定的信号状态在光学上是不活跃的，其形成动力学不容易使用时间分辨光学光谱，例如瞬时吸收(TA)光谱来探测。相比之下，时间分辨X射线散射技术对结构变化很敏感，与感兴趣状态的光学活性无关。例如，时间分辨小角X射线散射(tr-SAXS)对蛋白质在溶液中的大小和形状等全局结构变化很敏感，而时间分辨广角X射线散射(tr-WAXS)提供了关于蛋白质三级和四级结构变化的丰富信息，具有全局敏感性。因此，时间分辨X射线散射技术适合于探索BLUF结构域蛋白质中信号态形成的结构动力学。在这里，我们建议对Slr1694 BLUF结构域蛋白进行时间分辨实验，利用TR-SAXS和TR-WAXS技术来研究光化学反应导致信号态形成的机制。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. All living organisms have an ability to respond to biological stimuli such as light, voltage, oxygen, ligands and environmental factors. When applied, each stimulus is converted into a specific cellular response in several steps contributing to signal-transduction pathway. To understand the working mechanism of signal transduction, it is important to identify the molecular units involved in signaling, for example, stimuli receptors. Among the stimuli, light plays an important role in a wide range of biologically important cellular responses including photosynthesis and gene expression (1). Thus far, six kinds of photoreceptors have been identified (2). Among these photoreceptors, the BLUF domain was discovered recently, thus having been studied to a limited extent. In particular, the Slr1694 BLUF domain exists as a homo dimer in solution, but oligomerizes in the dark to form a decamer. This putative signaling state is optically inactive that its formation dynamics is not readily probed using time-resolved optical spectroscopy, for example, transient absorption (TA) spectroscopy. In contrast, time-resolved X-ray scattering techniques are sensitive to the structural changes regardless of the optical activity of the state of interest. For example, time-resolved small-angle X-ray scattering (TR-SAXS) is sensitive to global structural changes such as size and shape of a protein in solution, while time-resolved wide-angle X-ray scattering (TR-WAXS) provides rich information about tertiary and quaternary structural changes of a protein with global sensitivity. Therefore, time-resolved X-ray scattering techniques are suitable for probing the structural dynamics of the signaling state formation in the BLUF domain proteins. Here, we propose the time-resolved experiments on the Slr1694 BLUF domain proteins using TR-SAXS and TR-WAXS techniques to investigate the mechanism of photochemical reaction leading to the formation of signaling state.