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

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 (Delta tssS) 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.

Automated summary

This study reveals a unique virulence strategy of Yersinia pseudotuberculosis (Yptb) involving modulating the availability of the immunostimulatory metal ion Mn2+ in host cells. The Yptb T6SS delivers a micropeptide TssS into host cells to enhance virulence, but mutant strains lacking TssS show reduced virulence and stronger host innate immune responses. Furthermore, TssS functions as a Mn2+-chelating protein and inhibits the STING-mediated immune response by sequestering Mn2+, leading to bacterial immune evasion and sabotaged bacterial clearance in vivo.