Binding of the COOH-terminal lysine residue of streptokinase to plasmin(ogen) kringles enhances formation of the streptokinase.plasmin(ogen) catalytic complexes.
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.
Panizzi
Peter
P
Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2561, USA.
Boxrud
Paul D
PD
Verhamme
Ingrid M
IM
Bock
Paul E
PE
D000818:Animals; D020134:Catalytic Domain; D006801:Humans; D007700:Kinetics; D018082:Kringles; D008239:Lysine / Q000737:chemistry*; D008956:Models, Chemical; D010958:Plasminogen / Q000737:chemistry*; D010960:Plasminogen Activators / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013300:Streptokinase / Q000737:chemistry*; D013552:Swine
D010958:Plasminogen; D013300:Streptokinase; D010960:Plasminogen Activators; D008239:Lysine