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 <i>Yersinia pseudotuberculosis</i> (<i>Yptb</i>) involving modulation of the availability of Mn²⁺, an immunostimulatory metal ion in host cells. We showed that the <i>Yptb</i> type VI secretion system (T6SS) delivered a micropeptide, TssS, into host cells to enhance its virulence. The mutant strain lacking TssS (Δ<i>tssS</i>) 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 <i>Yptb</i> 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.