α-Enolase binds to human plasminogen on the surface of Bacillus anthracis

Abstract

α-Enolase of Bacillus anthracis has recently been classified as an immunodominant antigen and a potent virulence factor determinant. α-enolase (2-phospho-D-glycerate hydrolase (EC 4.2.1.11), a key glycolytic metalloenzyme catalyzes the dehydration of D-(+)-2-phosphoglyceric acid to phosphoenolpyruvate. Interaction of surface bound a-enolase with plasminogen has been incriminated in tissue invasion for pathogenesis. B. anthracis α-enolase was expressed in Escherichia coli and the recombinant enzyme was purified to homogeneity that exhibited a K_m of 3.3 mM for phosphoenolpyruvate and a V_max of 0.506 μMmin⁻¹ mg⁻¹. B. anthracis whole cells and membrane vesicles probed with anti-enolase antibodies confirmed the surface localization of α-enolase. The specific interaction of α-enolase with human plasminogen (but not plasmin) evident from ELISA and the retardation in the native gel reinforced its role in plasminogen binding. Putative plasminogen receptors in B. anthracis other than enolase were also observed. This binding was found to be carboxypeptidase sensitive implicating the role of C-terminal lysine residues. The recombinant enolase displayed in vitro laminin binding, an important mammalian extracellular matrix protein. Plasminogen interaction conferred B. anthracis with a potential to in vitro degrade fibronectin and exhibit fibrinolytic phenotype. Therefore, by virtue of its interaction to host plasminogen and extracellular matrix proteins, α-enolase may contribute in augmenting the invasive potential of B. anthracis.