The binding of the Yersinia pseudotuberculosis and Yersinia enterocolitica invasin proteins to β1 integrin receptors allows internalization of these organisms by cultured cells. The C-terminal 192-residue superdomain of the Y. pseudotuberculosis invasin is necessary and sufficient for integrin recognition, while a region located outside, and N-terminal to, this superdomain strongly enhances the efficiency of bacterial uptake. Within the enhancer region is a domain called D2 that allows invasin-invasin interaction. To investigate the role of the enhancer region, bacterial cell binding and entry mediated by the Y. pseudotuberculosis invasin protein (invasinpstb) was compared to that of Y. enterocolitica invasin (invasinent), which lacks the D2 self-association domain. Invasinent was shown to be unable to promote self-interaction, using the DNA binding domain of λ repressor as a reporter. Furthermore, two genetically engineered in-frame deletion mutations that removed D2 from invasinpstb were significantly less proficient than wild-type invasinpstb at promoting uptake, although the amount of surface-exposed invasin as well as the cell binding capacity of the recombinant Escherichia coli strains remained similar. Competitive uptake assays showed that E. coli cells expressing invasinpstb had a significant advantage in the internalization process versus either E. coli cells expressing invasinent or the invasinpstb derivatives deleted for D2, further demonstrating the importance of invasin self-interaction for the efficiency of invasin-mediated uptake
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