Dynamic interaction of the <i>Yersinia pseudotuberculosis</i> type three secretion system proteins <scp>LcrV</scp> and <scp>LcrG</scp>

Yersinia pathogenicity is dependent on polarized translocation of effector proteins via the type III secretion system (T3SS). The tip complex situated on the needle structure of the T3SS is required for contact with the eukaryotic host membrane and is to an extent composed of pentameric LcrV. LcrV is a multifunctional protein that also acts as a regulator of the T3SS by virtue of forming a high-affinity complex in the cytoplasm with its chaperone, LcrG. By employing a structure-based approach centered on mass spectrometry, FRET and NMR spectroscopy, we demonstrated that the LcrV-LcrG complex is best described as a multivalent complex, and that the N-terminal domain of LcrV contributes by negatively affecting the LcrG binding affinity. The N-terminal domain of LcrV is dynamic and undergoes a conformational change to accommodate LcrG binding. ¹⁹F NMR spectroscopy analysis suggests that the conformational change is an intrinsic property of the protein, which agrees with a conformational selection model. An analysis of effector secretion into a culture supernatant demonstrated that the low synthesis and low secretion phenotypes of a LcrV mutant where the N-terminal domain has been removed are linked to the structure, interactions and stability of the LcrV N-terminal domain. In summary, our results add insights into the dynamics of LcrV and its complex with LcrG.