Plasmin(ogen)-binding α-Enolase from Streptococcus pneumoniae: Crystal Structure and Evaluation of Plasmin(ogen)-binding Sites

α-Enolases are ubiquitous cytoplasmic, glycolytic enzymes. In pathogenic bacteria, α-enolase doubles as a surface-displayed plasmin(ogen)-binder supporting virulence. The plasmin(ogen)-binding site was initially traced to the two C-terminal lysine residues. More recently, an internal nine-amino acid motif comprising residues 248 to 256 was identified with this function. We report the crystal structure of α-enolase from Streptococcus pneumoniae at 2.0 Å resolution, the first structure both of a plasminogen-binding and of an octameric α-enolase. While the dimer is structurally similar to other α-enolases, the octamer places the C-terminal lysine residues in an inaccessible, inter-dimer groove restricting the C-terminal lysine residues to a role in folding and oligomerization. The nine residue plasminogen-binding motif, by contrast, is exposed on the octamer surface revealing this as the primary site of interaction between α-enolase and plasminogen.