Bifidobacterial enolase, a cell surface receptor for human plasminogen involved in the interaction with the host.

The interaction with the host plasminogen/plasmin system represents a novel component in themolecular cross-talk between bifidobacteria and human host. Here, we demonstrated that theplasminogen-binding bifidobacterial speciesB. longum,B. bifidum,B. breveandB. lactissharethe key glycolytic enzyme enolase as a surface receptor for human plasminogen. Enolase wasvisualized on the cell surface of the model strainB. lactisBI07. The His-tagged recombinantprotein showed a high affinity for human plasminogen, with an equilibrium dissociation constant inthe nanomolar range. By site-directed mutagenesis we demonstrated that the interaction betweentheB. lactisBI07 enolase and human plasminogen involves an internal plasminogen-binding sitehomologous to that of pneumococcal enolase. According to our data, the positively chargedresidues Lys-251 and Lys-255, as well as the negatively charged Glu-252, of theB. lactisBI07enolase are crucial for plasminogen binding. Acting as a human plasminogen receptor, thebifidobacterial surface enolase is suggested to play an important role in the interaction processwith the host.