PNAS: Shen Xihui's team from Northwest A&F University and others reveal the important role of manganese ions in anti-bacterial natural immunity

Natural immunity senses pathogen invasion through pattern recognition receptors and activates downstream responses to resist pathogen infection
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STING (MITA/ERIS) is a cytoplasmic cyclized dinucleotide (CDN, including bacterial-specific c-di-GMP, c-di-AMP and cGAMPs with various connection methods) receptors
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CDN binds to STING on the cytoplasmic side and causes STING to translocate to the Golgi apparatus; while the sulfated glycosaminoglycans (sGAGs) synthesized in the Golgi body bind to amino acids in the Golgi body of STING and initiate STING multimerization, recruiting the kinase TBK1 , And finally induce the production of I-type interferon and other cytokines
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Since the discovery of c-di-GMP in A.
xylinum in 1987, the discovery of c-di-AMP in B.
subtilis (B.
subtilis) in 2008 and the discovery of Vibrio cholerae (V.
cholerae) in 20123 Since '3'-cGAMP, most bacteria have been known to produce these second messengers, which are essential for their proliferation, differentiation and infection
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As an important defense method, host cells produce receptors (here, STING protein) that can specifically recognize these products that are indispensable to bacteria, and activate the host's anti-bacterial natural immune response
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The bacterial type VI secretion system (T6SS, type VI secretion system) is one of the current research hotspots in the field of microbes.
It can deliver a variety of effector proteins to the extracellular environment, other bacteria or host cells, and resist stress and compete between bacteria.
And play an important role in the interaction with the host
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In 2017, Shen Xihui's laboratory discovered that Burkholderia Thailandensis (B.
thailandensis) T6SS mediates the transport of manganese ions by secreting a manganese ion-binding effector protein TseM, which promotes the ability of bacteria to resist oxidative stress and pathogenicity
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In 2018, Jiang Zhengfan's laboratory revealed that viral infection caused the release of manganese ions from different organelles in host cells, which strongly promoted the activation of the cGAS-STING pathway to resist viral infection
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These findings prompted them to further explore whether this type of T6SS effector protein with manganese ion binding function can regulate the host's natural immunity by affecting the manganese ion level in the host cell
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On October 9, 2021, the Jiang Zhengfan Laboratory of the Beijing University of Science and Technology, the Shen Xihui Laboratory of Northwest A&F University and the Zhou Dongsheng Laboratory of the Military Medical College jointly published an online publication titled T6SS in the Proceedings of the National Academy of Sciences (PNAS) The research paper translocates a micropeptide to suppress STING-mediated innate immunity by sequestering manganese has achieved a new breakthrough in the field of anti-bacterial innate immunity
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This study found that the gram-negative bacterium Y.
pseudotuberculosis (Yptb) T6SS can secrete a manganese ion-binding protein TssS (T6SS-secreted micropeptide suppressing STING) consisting of only 48 amino acids, which promotes the bacteria to manganese Uptake of ions
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The mutant strain with the deletion of this gene (ΔtssS) significantly reduced the pathogenicity of mice, and the bacterial load in different tissues and organs of mice infected with the ΔtssS strain was also significantly reduced
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Transcriptomics analysis found that compared with the wild-type strain, the expression of Type I-IFNs and IFN-stimulated genes (ISGs) in the cells infected with the ΔtssS strain was significantly increased, suggesting TssS It can inhibit the host anti-bacterial natural immune response; and after the manganese ion binding site in TssS is mutated, its ability to inhibit the natural immune system and its pathogenicity to mice is significantly reduced, indicating that the manganese ion binding ability of TssS inhibits it Innate immunity is essential
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Further research found that LPS (gram-negative bacteria cell wall component) treatment can significantly increase the cytoplasmic manganese ion concentration, but overexpression of TssS protein in the cell can inhibit the activation of STING and downstream genes induced by cGAMP/c-di-GMP Express
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Yersinia pseudotuberculosis (Yptb), Y.
pestis (Y.
pestis) and Y.
enterocolitica (Y.
enterocolitica) of the same genus all produce c-di-GMP which is very important for its survival and infection
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Previous studies have shown that manganese ions can significantly promote the combination of c-di-GMP and STING
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Consistent with this, after wild-type Yptb or ΔtssS mutants infect wild-type mice, the bacterial load of Yptb wild-type-infected mice is significantly higher than that of ΔtssS-infected mice; and when these two strains respectively infect STING-deficient mice At the time, the huge difference in bacterial load between the different infection groups was significantly reduced
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These results show that: on the one hand, the bacterial products LPS and c-di-GMP induce the release of manganese ions in the host cell and jointly promote the activation of STING; on the other hand, the bacteria produce and secrete TssS by chelating intracellular manganese ions to weaken c-di- The ability of GMP to bind and activate STING can inhibit the host's natural immune response against bacteria
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TssS chelates manganese ions to inhibit the STING-mediated anti-bacterial natural immune response in host cells.
Unlike other known bacterial effectors, they usually interact with host intracellular proteins, nucleic acids and other macromolecules to cause disease in a different way.
This study reveals A bacterial effector protein chelates manganese ions in the host cell, thereby inhibiting the host's new mechanism of natural immune response
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As a new bacterial immune escape mechanism, this research provides a new perspective for understanding the role of T6SS in the pathogenic mechanism of bacteria.
It is not only important for understanding the molecular mechanism of pathogenic microorganisms regulating host immune response, but also for treatment.
Some diseases caused by over-activation of the autoimmune system provide new ideas
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More importantly, similar Mn2+ binding proteins with unknown functions have been identified in the T6SS gene clusters of a large number of different species of bacteria, suggesting that the natural immune escape mechanism discovered in this study is a ubiquitous and ancient anti-host response mechanism in bacteria.

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Postdoctoral fellows Zhu Lingfang and Xu Lei of Northwest University of Agriculture and Forestry Science and Technology, and postdoctoral fellow of Peking University School of Biological Sciences Wang Chenguang are the co-first authors of this paper.
Shen Xihui, Jiang Zhengfan and Zhou Dongsheng are co-corresponding authors
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This research has won the "Peking University-Tsinghua Life Sciences Joint Center", the Ministry of Education Key Laboratory of "Cell Proliferation and Differentiation" at Peking University, the National Key Research and Development Program, the National Natural Science Foundation of China, the China Postdoctoral Science Foundation and the Northwest Agriculture and Forestry University.
Funding for projects such as group construction plans
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Original link: https://doi.
org/10.
1073/pnas.
2103526118 Open for reprinting, welcome to forward to Moments and WeChat groups