Fig 8. Model of T6SS-4-facilitated Zn²⁺ transportation and oxidative resistance in Yptb.

OxyR activated by oxidative signals binds to the operator in the promoter of T6SS-4 to activate the expression of the system and its substrate YezP, leading to the production and assembly of the system, which translocates YezP into the extracellular milieu. YezP form a complex with Zn²⁺ to deliver the ions into the cell via a yet unknown mechanism. Intracellular Zn²⁺ mitigates the hydroxyl radicals or potentially other cell damaging processes to make the cells resistant to diverse environmental challenges.