Sun Zhe, Chen Yixiong, Yang Chen, Yang Sheng, Gu Yang, Jiang Weihong
Key Laboratory of Synthetic Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
Mol Microbiol. 2015 Feb;95(4):576-89. doi: 10.1111/mmi.12894. Epub 2014 Dec 20.
D-Xylose is the most abundant fermentable pentose in nature and can serve as a carbon source for many bacterial species. Since D-xylose constitutes the major component of hemicellulose, its metabolism is important for lignocellulosic biomass utilization. Here, we report a six-protein module for D-xylose signaling, uptake and regulation in solvent-producing Clostridium beijerinckii. This module consists of a novel 'three-component system' (a putative periplasmic ABC transporter substrate-binding protein XylFII and a two-component system LytS/YesN) and an ABC-type D-xylose transporter XylFGH. Interestingly, we demonstrate that, although XylFII harbors a transmembrane domain, it is not involved in D-xylose transport. Instead, XylFII acts as a signal sensor to assist the response of LytS/YesN to extracellular D-xylose, thus enabling LytS/YesN to directly activate the transcription of the adjacent xylFGH genes and thereby promote the uptake of D-xylose. To our knowledge, XylFII is a novel single transmembrane sensor that assists two-component system to respond to extracellular sugar molecules. Also of significance, this 'three-component system' is widely distributed in Firmicutes, indicating that it may play a broad role in this bacterial phylum. The results reported here provide new insights into the regulatory mechanism of D-xylose sensing and transport in bacteria.
D-木糖是自然界中含量最丰富的可发酵戊糖，可作为许多细菌物种的碳源。由于D-木糖是半纤维素的主要成分，其代谢对于木质纤维素生物质的利用至关重要。在此，我们报道了一个由六种蛋白质组成的模块，用于产溶剂拜氏梭菌中D-木糖的信号传导、摄取和调控。该模块由一个新型的“三组分系统”（一种假定的周质ABC转运体底物结合蛋白XylFII和一个双组分系统LytS/YesN）以及一个ABC型D-木糖转运体XylFGH组成。有趣的是，我们证明，尽管XylFII含有一个跨膜结构域，但它不参与D-木糖的转运。相反，XylFII作为信号传感器，协助LytS/YesN对细胞外D-木糖作出反应，从而使LytS/YesN能够直接激活相邻的xylFGH基因的转录，进而促进D-木糖的摄取。据我们所知，XylFII是一种新型的单跨膜传感器，可协助双组分系统对细胞外糖分子作出反应。同样重要的是，这种“三组分系统”在厚壁菌门中广泛分布，表明它可能在该细菌门中发挥广泛作用。本文报道的结果为细菌中D-木糖感知和转运的调控机制提供了新的见解。
