Research Project
9060389
? 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.
