Ligand Binding and Signaling State of Anabaena Sensory Rhodopsin Transducer

 描述(申请人提供)：与离子泵细菌视紫红质同系物不同，微生物感觉视紫红质-转导分子复合体为探索信号级联中蛋白质-蛋白质相互作用的化学提供了一个关键范例。2003年，淡水蓝藻Anabaena(Nostoc)sp.PCC7120发现了一种编码感觉性视紫红质类似物的染色体基因。与嗜盐古菌感觉性视紫红质不同，它不含任何膜转导基因产物。然而，一个相邻的基因产物被认为是这种光感受器的可溶性转导分子。光激活受体介导的信号传导的详细分子机制尚不清楚。提出的模型与任何已知的基于微生物感官的“趋光性”无关。然而，它类似于视觉光感受器、视紫红质以及其他通过细胞质成分耦合的G蛋白信号。因此，这种可溶的转导蛋白的作用可能会建立一种新的信号转导模式，这一模式与嗜盐古细菌和真核生物所共有。有趣的是，这种假定的可溶性转导分子存在于一系列不含感觉性视紫红光感受器的微生物物种中。序列和结构折叠同源性揭示了这种分子没有任何既定的功能特征。基因组数据库搜索显示，它们存在于广泛的微生物种群中，包括各种病原体。存在于其他序列中的转导子的同源序列被称为“未知功能域”家族。这一家族包括病原体，如热带菌、放线菌和热裂杆菌。光感受器和可能的换能器的原子分辨结构都是可用的。基于结构基序的生物信息学分析表明，该转导同源物可能属于微生物小碳水化合物结合域超家族的成员。它很可能在一个独特的β三明治框架中作为一个新的碳水化合物结合模块。我们的初步数据，基于单极定位，表明与细菌纤维素合成蛋白有很强的相关性和亲和力，这种蛋白特异性地定位在极点。最近的核磁共振研究表明，该转导分子与DNA之间存在类似于真核的相互作用。此外，基于序列的分析预测以及Pi工作的初始数据支持转导蛋白的磷接受特性。此外，磷酸化导致损害转导的异常稳定性，这表明它在信号转导中可能发挥作用。这个假定的转导蛋白的不寻常的稳定组装和它的分离将阐明这一信号状态。 Duf蛋白分子。本项目旨在将转导蛋白作为磷受体模块的功能状态与糖结合基序的存在联系起来，并表征这种特征对受体结合的调节作用。对转导分子信号状态的研究将加深我们对包括各种病原体在内的其他DUF成员的了解。

 DESCRIPTION (provided by applicant): Unlike to ion pump bacteriorhodopsin homologues, microbial sensory rhodopsin-transducer molecular complexes served a key paradigm for exploring the chemistry of protein-protein interaction in signaling cascade. In 2003, freshwater cyanobacterium Anabaena (Nostoc) sp. PCC 7120 revealed a chromosomal gene encoding a sensory rhodopsin analogue. In contrast to haloarchaeal sensory rhodopsin, it does not contain any membrane transducer gene product. However, an adjacent gene product is indicated to be a soluble transducer molecule for this photoreceptor. The detailed molecular mechanism of photoactivated receptor mediated signaling is not known. The proposed model is not related to any known microbial sensory based "phototaxis". However, it is analogous to visual photoreceptor, rhodopsin and to other G- protein coupled signaling via cytoplasmic components. Thus the role of this soluble putative transducer protein may establish a novel mode of signaling as shared by haloarchaea and eukarya. Interestingly, this putative soluble transducer molecule is present in a series of microbial species that do not contain sensory rhodopisn photoreceptor. Sequential and structural fold homology reveals such molecule without any established functional feature. Genome database search revealed their presence in broad microbial population including various pathogens. The homologue sequence of a transducer present in other sequences is referred to as "domain of unidentified function" [DUF], family. This family includes pathogens, such as Tropheryma, Actinomyces and Thermobifida. The atomic resolution structures of both photoreceptor and putative transducer are available. Structural motif based bioinformatics analysis has revealed that the transducer homologue may be classified as a member of a super family of microbial small carbohydrate binding domain. It is likely that it may serve as a novel carbohydrate binding module in a unique beta sandwich framework. Our preliminary data, based on unipolar localization suggests strong correlation and affinity to bacterial cellulose synthesis proteins that specifically localizes at pole. Recent NMR study has shown a eukaryotic like interaction of this transducer with DNA. Further, sequence- based analysis prediction along with initial data from PI's work supports the phosphor-accepting property of the transducer protein. Additionally, the phosphorylation leads to impair the unusual stability of transducer, suggesting its putative role in signaling. The unusual stable assembly and its segregation of this putative transducer protein would elucidate the signaling state of this DUF protein molecule. This project is aimed to relate the functional state of transducer as a phosphor-acceptor module and presence of a sugar binding motif and characterize the modulation of such a feature on receptor binding. The characterization of transducer's signaling state would broaden our understanding towards other DUF members including various pathogens as well.