C-Terminal Lysine Residue of Pneumococcal Triosephosphate Isomerase Contributes to Its Binding to Host Plasminogen

Abstract

The main causative agent of pneumonia, Streptococcus pneumoniae, is also responsible for invasive diseases. S. pneumoniae recruits human plasminogen for the invasion and colonization of host tissues. We previously discovered that S. pneumoniae triosephosphate isomerase (TpiA), an enzyme involved in intracellular metabolism that is essential for survival, is released extracellularly to bind human plasminogen and facilitate its activation. Epsilon-aminocaproic acid, a lysine analogue, inhibits this binding, suggesting that the lysine residues in TpiA are involved in plasminogen binding. In this study, we generated site-directed mutant recombinants in which the lysine residue in TpiA was replaced with alanine and analyzed their binding activities to human plasminogen. Results from blot analysis, enzyme-linked immunosorbent assay, and surface plasmon resonance assay revealed that the lysine residue at the C-terminus of TpiA is primarily involved in binding to human plasminogen. Furthermore, we found that TpiA binding to plasminogen through its C-terminal lysine residue was required for the promotion of plasmin activation by activating factors.

The Pneumococcal Protein SufC Binds to Host Plasminogen and Promotes Its Conversion into Plasmin

“…Among the proteins expressed by S. pneumoniae, Eno [28][29][30][31][32][33][34], GAPDH [35], cholinebinding protein E (CbpE) [45], plasmin-and fibronectin-binding protein A (PfbA) [46], plasminogen-and fibronectin-binding protein B (PfbB) [47], endopeptidase O (PepO) [48], Tuf [36], phosphoglycerate kinase [49], pneumococcal surface protein C (PspC) [50], TpiA [15,51], ClpC [17], and UvrC [17] bind plasminogen. A few of these, including Eno [28], CbpE [45], PepO [48], Tuf [36], and TpiA [15], use lysine residues in the protein molecule to bind to plasminogen.…”

“…A few of these, including Eno [28], CbpE [45], PepO [48], Tuf [36], and TpiA [15], use lysine residues in the protein molecule to bind to plasminogen. A recent study on TpiA reported that the plasminogen binding site was located at the C-terminus [51]. In Eno, which has been studied the most, the binding site for plasminogen has been identified as two C-terminal lysine residues and the nine-amino acid motif FYDKERKVY, located at positions 248-256 [30].…”

“…site was located at the C-terminus [51]. In Eno, which has been studied the most, the binding site for plasminogen has been identified as two C-terminal lysine residues and the nine-amino acid motif FYDKERKVY, located at positions 248-256 [30].…”