Pathogenic Yersinia all harbor a virulence plasmid-encoded Ysc-Yop T3SS. In this system, translocator function is performed by the hydrophobic proteins YopB and YopD. With the goal to better understand how YopD orchestrates yop-regulatory control, translocon pore formation and Yop effector translocation, we performed an in silico prediction of coiled-coil motifs in YopD and YopD-like sequences from other bacteria. Of interest was a predicted N-terminal coiled-coil that occurred solely in Yersinia YopD sequences. To investigate if this unique feature was biologically relevant, two in cis point mutations were generated with a view to disrupting this putative structure. Both mutants maintained full T3SS function in vitro in terms of environmental control of Yops synthesis and secretion, effector toxin translocation and evasion of phagocytosis and killing by cultured immune cells. However, these same mutants were attenuated for virulence in a murine oral-infection model. The cause of this tardy disease progression is unclear. However, these data indicate that any structural flaw in this element unique to the N-terminus will subtly compromise an aspect of YopD biology. Sub-optimal T3SSs are then formed that are unable to fortify Yersinia against attack by the host innate and adaptive immune response.
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