Bifidobacterium lactis Enolase, surface localization and mechanism of interaction with human Plasminogen

The glycolytic enzyme enolase has been identified as putative plasminogen (Plg) binding protein in B. lactis BI07. Since enolase represents one of the best characterized Plg receptors in prokaryotes and eukaryotes, here we characterized this B. lactis housekeeping enzyme with respect to surface localization and Plg binding activity. The display of enolase on B. lactis BI07 cell surface was proved by immunoelectron microscopy. In order to individuated the putative Plg binding sites of B. lactis enolase, an high quality homology model was generated. The B. lactis enolase possesses structural homologue of the internal Plg binding site BS2 of pneumococcal enolase, as well as a C-terminal lysine, which constitute the Plg binding site BS1. In order to characterize the mechanism of Plg binding of B. lactis enolase, the wild type protein, as well as the protein mutated in the BS2, BS1, and BS2/BS1 homologues, were purified and their Plg binding activity evaluated. According to our preliminary data, the homologue of BS2 represents an essential Plg binding site of B. lactis BI07 enolase whereas the homologue of BS1 is only marginally involved.