Scientists Reveal the Mechanism of Environmental D-xylose Perception in Bacterial

One of the major constituents of plant biomass, D-xylose, has been considered as an attractive carbon source for bio-based fuel and chemical production through fermentation. But for years people did not know how the environmental D-xylose signal is sensed by the bacteria and metabolize D-xylose in detail.

In 2015, a membrane two-component complex was identified in Firmicutes bacteria, comprising a membrane-associated sensor protein (XylFII), a transmembrane histidine kinase (LytS) for periplasmic d-xylose sensing, and a cytoplasmic response regulator (YesN) that activates the transcription of the target ABC transporter XylFGH genes to promote the uptake of d-xylose. However, the molecular mechanism underlying signal perception and integration of these processes remains unclear.

In a recent study published in PNAS, a research team led by Profs. ZHANG Peng and JIANG Weihong at Institute of Plant Physiology and Ecology of Chinese Academy of Sciences determined the structures of the XylFII-LytSN (N-terminal periplasmic domain of LytS) complex in its d-xylose free and d-xylose bound forms, which together with biochemical and physiological methods demonstrated the D-xylose sensing mechanism through XylFII-LytS in bacteria.

Researchers found that LytSN contains a four-helix bundle, and XylFII contains two Rossmann fold-like globular domains with a xylose binding cleft between them. In the absence of d-xylose, LytSN and XylFII can form a heterodimer.

Specific binding of d-xylose to the cleft of XylFII will induce a large conformational change that will close the cleft and bring the globular domains closer together. This conformational change can lead to the formation of an active XylFII-LytS heterotetramer, which activates the downstream response regulator and the expression of the d-xylose ABC transporter XylFGH.

They further revealed that mutations at the d-xylose binding site and the heterotetramer interface will diminish heterotetramer formation and impair the d-xylose–sensing function of XylFII-LytS. Based on these data, a working model of XylFII-LytS was proposed that can provides a molecular basis for d-xylose utilization and metabolic modification in bacteria.

Hopefully, this study will contribute to the development of d-xylose utilization and metabolic engineering in bacteria.

This work was funded by the National Natural Science Foundation of China, and Chinese Academy of Sciences.

Article website: http://www.pnas.org/content/early/2017/07/14/1620183114.abstract

Figure: Mechanism of d-xylose perception by the membrane two-component complex XylFII-LytS.

AUTHOR CONTACT:
Zhang Peng, Principal Investigator
National Key Laboratory of Plant Molecular Genetics
CAS Center for Excellence in Molecular Plant Sciences
Institute of Plant Physiology and Ecology
Shanghai Institutes for Biological Sciences
Chinese Academy of Sciences
300 Fenglin Road
Shanghai 200032
Phone: (86) 21-54924219
Email: pengzhang01@sibs.ac.cn

Jiang Weihong, Principal Investigator
CAS Key Laboratory of Synthetic Biology
Institute of Plant Physiology and Ecology
Shanghai Institutes for Biological Sciences
Chinese Academy of Sciences
300 Fenglin Road
Shanghai 200032
Phone: (86) 21-54924172
Email: whjiang@sibs.ac.cn