title: The Anabaena sensory rhodopsin transducer defines a novel superfamily of prokaryotic small-molecule binding domains.
abstract: The Anabaena sensory rhodopsin transducer (ASRT) is a small protein that has been claimed to function as a signaling molecule downstream of the cyanobacterial sensory rhodopsin. However, orthologs of ASRT have been detected in several bacteria that lack rhodopsin, raising questions about the generality of this function. Using sequence profile searches we show that ASRT defines a novel superfamily of beta-sandwich fold domains. Through contextual inference based on domain architectures and predicted operons and structural analysis we present strong evidence that these domains bind small molecules, most probably sugars. We propose that the intracellular versions like ASRT probably participate as sensors that regulate a diverse range of sugar metabolism operons or even the light sensory behavior in Anabaena by binding sugars or related metabolites. We also show that one of the extracellular versions define a predicted sugar-binding structure in a novel cell-surface lipoprotein found across actinobacteria, including several pathogens such as Tropheryma, Actinomyces and Thermobifida. The analysis of this superfamily also provides new data to investigate the evolution of carbohydrate binding modes in beta-sandwich domains with very different topologies.
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA. desouza@ncbi.nlm.nih.gov
authors.forename: Robson F
authors.initials: RF
authors.lastname: De Souza
authors.forename: Lakshminarayan M
authors.initials: LM
authors.lastname: Iyer
authors.forename: L
authors.initials: L
authors.lastname: Aravind
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D025603:Sensory Rhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D025603:Sensory Rhodopsins
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