TY - JOUR
T1 - α Domain deletion converts sreptokinase into a fibrin-dependent plasminogen activator through mechanisms akin to staphylokinase and tissue plasminogen activator
AU - Sazonova, Irina Y.
AU - Robinson, Brian R.
AU - Gladysheva, Inna P.
AU - Castellino, Francis J.
AU - Reed, Guy L.
PY - 2004/6/11
Y1 - 2004/6/11
N2 - The mechanism of action of plasminogen (Pg) activators may affect their therapeutic properties in humans. Streptokinase (SK) is a robust Pg activator in physiologic fluids in the absence of fibrin. Deletion of a "catalytic switch" (SK residues 1-59), alters the conformation of the SK α domain and converts SKΔ59 into a fibrin-dependent Pg activator through unknown mechanisms. We show that the SK α domain binds avidly to the Pg kringle domains that maintain Glu-Pg in a tightly folded conformation. By virtue of deletion of SK residues 1-59, SKΔ59 loses the ability to unfold Glu-Pg during complex formation and becomes incapable of nonproteolytic active site formation. In this manner, SKΔ59 behaves more like staphylokinase than like SK; it requires plasmin to form a functional activator complex, and in this complex SKΔ59 does not protect plasmin from inhibition by α2-antiplasmin. At the same time, SKΔ59 is unlike staphylokinase or SK and is more like tissue Pg activator, because it is a poor activator of the tightly folded form of Glu-Pg in physiologic solutions. SKΔ59 can only activate Glu-Pg when it was unfolded by fibrin interactions or by Cl--deficient buffers. Taken together, these studies indicate that an intact α domain confers on SK the ability to nonproteolytically activate Glu-Pg, to unfold and process Glu-Pg substrate in physiologic solutions, and to alter the substrate-inhibitor interactions of plasmin in the activator complex. The loss of an intact α domain makes SKΔ59 activate Pg through classical "fibrin-dependent mechanisms" (akin to both staphylokinase and tissue Pg activator) that include: 1) a marked preference for a fibrin-bound or unfolded Glu-Pg substrate, 2) a requirement for plasmin in the activator complex, and 3) the creation of an activator complex with plasmin that is readily inhibited by α 2-antiplasmin.
AB - The mechanism of action of plasminogen (Pg) activators may affect their therapeutic properties in humans. Streptokinase (SK) is a robust Pg activator in physiologic fluids in the absence of fibrin. Deletion of a "catalytic switch" (SK residues 1-59), alters the conformation of the SK α domain and converts SKΔ59 into a fibrin-dependent Pg activator through unknown mechanisms. We show that the SK α domain binds avidly to the Pg kringle domains that maintain Glu-Pg in a tightly folded conformation. By virtue of deletion of SK residues 1-59, SKΔ59 loses the ability to unfold Glu-Pg during complex formation and becomes incapable of nonproteolytic active site formation. In this manner, SKΔ59 behaves more like staphylokinase than like SK; it requires plasmin to form a functional activator complex, and in this complex SKΔ59 does not protect plasmin from inhibition by α2-antiplasmin. At the same time, SKΔ59 is unlike staphylokinase or SK and is more like tissue Pg activator, because it is a poor activator of the tightly folded form of Glu-Pg in physiologic solutions. SKΔ59 can only activate Glu-Pg when it was unfolded by fibrin interactions or by Cl--deficient buffers. Taken together, these studies indicate that an intact α domain confers on SK the ability to nonproteolytically activate Glu-Pg, to unfold and process Glu-Pg substrate in physiologic solutions, and to alter the substrate-inhibitor interactions of plasmin in the activator complex. The loss of an intact α domain makes SKΔ59 activate Pg through classical "fibrin-dependent mechanisms" (akin to both staphylokinase and tissue Pg activator) that include: 1) a marked preference for a fibrin-bound or unfolded Glu-Pg substrate, 2) a requirement for plasmin in the activator complex, and 3) the creation of an activator complex with plasmin that is readily inhibited by α 2-antiplasmin.
UR - http://www.scopus.com/inward/record.url?scp=2942590331&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=2942590331&partnerID=8YFLogxK
U2 - 10.1074/jbc.M400253200
DO - 10.1074/jbc.M400253200
M3 - Article
C2 - 15069059
AN - SCOPUS:2942590331
SN - 0021-9258
VL - 279
SP - 24994
EP - 25001
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 24
ER -