Surface-associated phosphoglycerate kinase (PGK) of Staphylococcus aureus binds human plasminogen in a partially lysine-independent manner.

Abstract

Staphylococcus aureus, a potent opportunistic pathogen causes a variety of infections ranging from mild skin infections to life-threatening diseases. With the rapid increase in antimicrobial resistant pathogens, it is critical to comprehensively understand the virulence strategies employed by the pathogen to invade the host. The glycolytic enzymes of S. aureus have been reported to possess additional roles promoting pathogenesis. In this study, we cloned, overexpressed and purified the S. aureus glycolytic protein, phosphoglycerate kinase (PGK) (EC 2.7.2.3) and investigated its localization and interaction with human plasminogen. To elucidate the localization of PGK, a whole cell ELISA and cell fractionation was performed. We report the localization of the wild type protein in the cytosol as well as the cell surface associated fractions of S. aureus. Whole-cell ELISA with anti-PGK antibodies showed significant antibody binding compared to control with secondary antibody (∼11-fold increase, p = 0.0005), indicating surface exposure of PGK. Purified recombinant PGK bound human plasminogen (p < 0.0001) and enhanced its conversion to its active form in the presence of tissue plasminogen activator (p < 0.0001). Plasminogen binding to PGK was only partially inhibited by ε-aminocaproic acid, indicating that lysine-mediated interactions are not the sole determinants. These results were fully corroborated with the molecular dynamics which revealed stable binding throughout the entire 500ns period and a similar disposition of the lysines. These findings suggest that PGK may function as a moonlighting protein, playing an essential role in the interaction of S. aureus with its host through plasminogen binding.