De Souza Robson F, Iyer Lakshminarayan M, Aravind L
National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
Biol Direct. 2009 Aug 14;4:25; discussion 25. doi: 10.1186/1745-6150-4-25.
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.
鱼腥藻感光视紫红质转导蛋白（ASRT）是一种小蛋白，据称其在蓝藻感光视紫红质下游作为信号分子发挥作用。然而，在几种缺乏视紫红质的细菌中检测到了ASRT的直系同源物，这引发了关于该功能普遍性的疑问。通过序列谱搜索，我们表明ASRT定义了一个新型的β-折叠结构域超家族。基于结构域结构、预测的操纵子和结构分析进行上下文推断，我们提供了有力证据，证明这些结构域结合小分子，很可能是糖类。我们提出，像ASRT这样的细胞内版本可能作为传感器参与其中，通过结合糖类或相关代谢物来调节多种糖类代谢操纵子，甚至调节鱼腥藻中的光感行为。我们还表明，一种细胞外版本在放线菌（包括嗜肺军团菌、放线菌和嗜热栖热放线菌等几种病原体）中发现的一种新型细胞表面脂蛋白中定义了一种预测的糖结合结构。对这个超家族的分析也为研究具有非常不同拓扑结构的β-折叠结构域中碳水化合物结合模式的进化提供了新数据。
