Identification of the multiple roles of enolase as an plasminogen receptor and adhesin in Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the etiological agent underlying porcine enzootic pneumonia, a chronic respiratory disease worldwide. The recruitment of plasminogen to the surface and subsequently promotion of plasmin conversion by the surface-located receptor, have been reported to assist the adhesion and invasion of Mycoplasmas. The surface localization and plasminogen-binding ability of M. hyopneumoniae enolase were previously confirmed; however, the biological functions were not be determined, especially the role as a plasminogen receptor. Here, using ELISA and SPR analyses, we confirmed the stable binding of M. hyopneumoniae enolase to plasminogen in a dose-dependent manner. The facilitation of the activation of plasminogen in the presence of tPA and direct activation of plasminogen at low efficiency without tPA addition by M. hyopneumoniae enolase were also determined using a plasmin-specific chromogenic substrate. Notably, the C-terminal and N-terminal regions located in M. hyopneumoniae enolase play an important role in plasminogen binding and activation. Additionally, we demonstrate that M. hyopneumoniae enolase can competitively inhibit the adherence of M. hyopneumoniae to PK15 cells. These results provide insight into the role of enolase in M. hyopneumoniae infection, a mechanism that manipulates the proteolytic system of the host.