High-resolution cryo-EM analysis of a Streptococcus pyogenes M-protein/human plasminogen complex

The importance of human plasminogen (hPg)/plasmin (hPm)/cell receptor complexes in invasiveness of cells has been amply established. The objective of this investigation was to determine a high-resolution structure of a major Group A Streptococcus (GAS) bacterial receptor (PAM) for hPg/hPm when bound on a cell surface to its major ligand, hPg. As a model cell surface with endogenous PAM, we employed engineered PAM-expressing lentivirus (LV) particles. We show that the ectodomain of a PAM-type M-Protein (M-Prt), in complex with hPg, is folded through distinct intra- and inter-domain interactions to a more compact form on the cell surface, thus establishing a new paradigm for membrane-bound M-Prt/ligand structures. These studies provide a framework for addressing the need for treatments of GAS disease by providing a molecular platform to solve structures of virulence-determining membrane proteins.