The Type VI Secretion System Engages a Redox-Regulated Dual-Functional Heme Transporter for Zinc Acquisition

Publication date: 25 July 2017
Source:Cell Reports, Volume 20, Issue 4
Author(s): Meiru Si, Yao Wang, Bing Zhang, Chao Zhao, Yiwen Kang, Haonan Bai, Dawei Wei, Lingfang Zhu, Lei Zhang, Tao G. Dong, Xihui Shen
The type VI secretion system was recently reported to be involved in zinc acquisition, but the underlying mechanism remains unclear. Here, we report that Burkholderia thailandensis T6SS4 is involved in zinc acquisition via secretion of a zinc-scavenging protein, TseZ, that interacts with the outer membrane heme transporter HmuR. We find that HmuR is a redox-regulated dual-functional transporter that transports heme iron under normal conditions but zinc upon sensing extracellular oxidative stress, triggered by formation of an intramolecular disulfide bond. Acting as the first line of defense against oxidative stress, HmuR not only guarantees an immediate response to the changing environment but also provides a fine-tuned mechanism that allows a gradual response to perceived stress. The T6SS/HmuR-mediated active zinc transport system is also involved in bacterial virulence and contact-independent bacterial competition. We describe a sophisticated bacterial zinc acquisition mechanism affording insights into the role of metal ion transport systems.

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Teaser

Si et al. find that T6SS4 secretes a proteinaceous zincophore, TseZ, that interacts with the outer membrane heme transporter HmuR to acquire zinc under oxidative stress. HmuR is a dual-function transporter, transporting heme under normal conditions but zinc upon sensing extracellular oxidative stress, triggered by forming an intramolecular disulfide bond.


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