T6SS translocates a micropeptide to suppress STING-mediated innate immunity by sequestering manganese

Abstract

Cellular ionic concentrations are a central factor orchestrating host innate immunity, but no pathogenic mechanism that perturbs host innate immunity by directly targeting metal ions has yet been described. Here, we report a unique virulence strategy of Yersinia pseudotuberculosis (Yptb) involving modulation of the availability of Mn2+, an immunostimulatory metal ion in host cells. We showed that the Yptb type VI secretion system (T6SS) delivered a micropeptide, TssS, into host cells to enhance its virulence. The mutant strain lacking TssS (ΔtssS) showed substantially reduced virulence but induced a significantly stronger host innate immune response, indicating an antagonistic role of this effector in host antimicrobial immunity. Subsequent studies revealed that TssS is a Mn2+-chelating protein and that its Mn2+-chelating ability is essential for the disruption of host innate immunity. Moreover, we showed that Mn2+ enhances the host innate immune response to Yptb infection by activating the stimulator of interferon genes (STING)-mediated immune response. Furthermore, we demonstrated that TssS counteracted the cytoplasmic Mn2+ increase to inhibit the STING-mediated innate immune response by sequestering Mn2+. Finally, TssS-mediated STING inhibition sabotaged bacterial clearance in vivo. These results reveal a previously unrecognized bacterial immune evasion strategy involving modulation of the bioavailability of intracellular metal ions and provide a perspective on the role of the T6SS in pathogenesis.

Manganese Utilization in Salmonella Pathogenesis: Beyond the Canonical Antioxidant Response

“…Salmonella T6SS is activated by oxidative stress and our bioinformatics analysis has revealed a conserved locus in the Salmonella genome with high similarity to Burkholderia MnoT ( Figures 1B,D ) ( Kroger et al, 2013 ). Additional T6SS substrates with Mn 2+ -scavenging capacities are still being uncovered, including the TssS micropeptide from Yersinia pseudotuberculosis that chelates Mn 2+ and sabotages bacterial clearance by inhibiting STING-mediated innate immune response ( Zhu et al, 2021 ).…”

Regulation of Bacterial Manganese Homeostasis and Usage During Stress Responses and Pathogenesis

“…These data suggest an underappreciated role for OMPs in Mn import and overall Mn homeostasis. A novel metal transport mechanism using T6SS effectors (TseM and TssS), together with an additional outer membrane TonBdependent Mn transporter (MnoT), has also recently been described (Si et al, 2017;Yang et al, 2021;Zhu et al, 2021). In Burkholderia, TseM is secreted into the extracellular environment, where it specifically binds Mn and delivers it to MnoT for transport (Si et al, 2017).…”

“…The small protein TssS produced by Yersinia is delivered into mammalian host cells, where it sequesters Mn. TssS-mediated Mn chelation reduces activity of the Mn-dependent enzyme cGAS, which activates the STING pathway of the innate immune response (Wang et al, 2018;Zhu et al, 2021). It is unclear if TssS also mediates Mn import into bacterial cells or if it primarily remains in the host cytoplasm in its Mn chelator role.…”

“…It is unclear if TssS also mediates Mn import into bacterial cells or if it primarily remains in the host cytoplasm in its Mn chelator role. Bacterial virulence and/or intracellular survival is reduced in both systems when the effectors or OM transporter are deleted (Si et al, 2017;Zhu et al, 2021). It will be interesting to see if additional Mn-binding proteins are found, as T6SS effector proteins are poorly characterized.…”

Mitochondrion‐located peptides and their pleiotropic physiological functions

“…The micropeptides, often fewer than 100 amino acids (AAs) (occasionally up to 200 AAs), are widely distributed among tissues, and some of them show a high degree of conservation among species. Up to now, only a limited number of micropeptides have been clearly characterized, which are shown to participate in a broad range of cellular functions including immunity [11][12][13], development [14][15][16], tumor intervention [17,18], muscle biology [19][20][21][22][23][24], stress signaling [25,26], metabolism [27][28][29][30][31], and so on. Interestingly, among all known micropeptides, membrane-localized ones compose a large proportion and act as components of the organelle membrane or the plasma membrane [32].…”