Abstract
Streptokinase (SK) activates human fibrinolysis by inducing non-proteolytic activation of the serine proteinase zymogen, plasminogen (Pg), in the SK.Pg* catalytic complex. SK.Pg* proteolytically activates Pg to plasmin (Pm). SK-induced Pg activation is enhanced by lysine-binding site (LBS) interactions with kringles on Pg and Pm, as evidenced by inhibition of the reactions by the lysine analogue, 6-aminohexanoic acid. Equilibrium binding analysis and [Lys]Pg activation kinetics with wild-type SK, carboxypeptidase B-treated SK, and a COOH-terminal Lys414 deletion mutant (SKDeltaK414) demonstrated a critical role for Lys414 in the enhancement of [Lys]Pg and [Lys]Pm binding and conformational [Lys]Pg activation. The LBS-independent affinity of SK for [Glu]Pg was unaffected by deletion of Lys414. By contrast, removal of SK Lys414 caused 19- and 14-fold decreases in SK affinity for [Lys]Pg and [Lys]Pm binding in the catalytic mode, respectively. In kinetic studies of the coupled conformational and proteolytic activation of [Lys]Pg, SKDeltaK414 exhibited a corresponding 17-fold affinity decrease for formation of the SKDeltaK414.[Lys]Pg* complex. SKDeltaK414 binding to [Lys]Pg and [Lys]Pm and conformational [Lys]Pg activation were LBS-independent, whereas [Lys]Pg substrate binding and proteolytic [Lys]Pm generation remained LBS-dependent. We conclude that binding of SK Lys414 to [Lys]Pg and [Lys]Pm kringles enhances SK.[Lys]Pg* and SK.[Lys]Pm catalytic complex formation. This interaction is distinct structurally and functionally from LBS-dependent Pg substrate recognition by these complexes.
Highlights
Streptokinase (SK)2 activates the human fibrinolytic system by activating the zymogen, plasminogen (Pg) to form the fibrin
LBS interactions with fibrin mediated by COOHterminal lysine residues localize and accelerate Pg activation carboxypeptidase B; 6-AHA; 6-aminohexanoic acid; pNA, p-nitroaniline; Pg, plasminogen; [Glu]Pg, compact form of Pg; [Lys]Pg, [Glu]Pg lacking the 77-residue NH2-terminal peptide; [Lys]Pm, Pm, plasmin; fluorescein-labeled analogues of Pg or Pm prepared with N␣-[(acetylthio)acetyl]-(D-Phe)Phe-Arg-CH2Cl and 5-(iodoacetamido)fluorescein are represented by [5F]FFR-Pg or –Pm; LBS, lysine-binding site; TEV, tobacco etch virus
Binding of Native SK and Carboxypeptidase B (CpB)-treated SK to [Lys]Pg—Native SK was treated with CpB to remove the COOH-terminal lysine residue, under conditions where there was no detectable degradation of SK observable by SDS-gel electrophoresis
Summary
Binding of the COOH-terminal Lysine Residue of Streptokinase to Plasmin(ogen) Kringles Enhances Formation of the Streptokinase1⁄7Plasmin(ogen) Catalytic Complexes*. We conclude that binding of SK Lys414 to [Lys]Pg and [Lys]Pm kringles enhances SK1⁄7[Lys]Pg* and SK1⁄7[Lys]Pm catalytic complex formation This interaction is distinct structurally and functionally from LBS-dependent Pg substrate recognition by these complexes. LBS interactions with fibrin mediated by COOHterminal lysine residues localize and accelerate Pg activation carboxypeptidase B; 6-AHA; 6-aminohexanoic acid; pNA, p-nitroaniline; Pg, plasminogen; [Glu]Pg, compact form of Pg; [Lys]Pg, [Glu]Pg lacking the 77-residue NH2-terminal peptide; [Lys]Pm, Pm, plasmin; fluorescein-labeled analogues of Pg or Pm prepared with N␣-[(acetylthio)acetyl]-(D-Phe)Phe-Arg-CH2Cl and 5-(iodoacetamido)fluorescein are represented by [5F]FFR-Pg or –Pm; LBS, lysine-binding site; TEV, tobacco etch virus. This interaction is shown to be structurally and functionally distinct from the LBS-dependent binding of [Lys]Pg as a substrate of the catalytic complexes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
