Functional interaction of plasminogen activator inhibitor type 1 (PAI-1) and heparin.
Plasminogen activator inhibitor type 1 (PAI-1), the fast-acting inhibitor of tissue-type plasminogen activator (t-PA) and urokinase (u-PA), is a member of the serpin superfamily of proteins. Both in plasma and in the growth substratum of cultured endothelial cells, PAI-1 is associated with its binding protein vitronectin, resulting in a stabilization of active PAI-1. Recently, it has been demonstrated that the PAI-1-binding site on vitronectin is adjacent to a heparin-binding site (Preissner et al., 1990). Furthermore, it can be deduced that the amino acid residues, proposed to mediate heparin binding in the serpins antithrombin III and heparin cofactor II, are conserved in PAI-1. Consequently, here we have investigated whether PAI-1 also interacts with heparin. At pH 7.4, PAI-1 quantitatively binds to heparin-Sepharose and can be eluted with increasing [NaCl]. Binding of PAI-1 to heparin-Sepharose can be efficiently competed with heparin in solution (IC50, 7 microM). In the presence of heparin, the protease specificity of PAI-1 toward thrombin is substantially increased. This is shown by (i) quenching of thrombin activity of PAI-1 in the presence of heparin and (ii) induction of the formation of SDS-stable complexes between thrombin and PAI-1 by heparin. In a dose response curve, both effects reached a maximum at approximately 1 unit/mL and then diminished again upon further increasing the heparin concentration, strongly suggesting a template mechanism as an explanation for the observed effect. In contrast to vitronectin, heparin does not stabilize the active conformation of PAI-1.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Molecular Biology, Central Laboratory of The Netherlands Red Cross Blood Transfusion Service, Amsterdam.
H J
HJ
Ehrlich
J
J
Keijer
K T
KT
Preissner
R K
RK
Gebbink
H
H
Pannekoek
D000345:Affinity Labels; D000595:Amino Acid Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D006023:Glycoproteins / Q000378:metabolism; D006493:Heparin / Q000378:metabolism*; D015844:Heparin Cofactor II; D006801:Humans; D008969:Molecular Sequence Data; D010960:Plasminogen Activators / Q000378:metabolism*; D015849:Plasminogen Inactivators / Q000378:metabolism*; D011487:Protein Conformation; D012685:Sepharose / Q000031:analogs & derivatives; D013917:Thrombin / Q000378:metabolism; D019096:Vitronectin
D000345:Affinity Labels; D006023:Glycoproteins; D015849:Plasminogen Inactivators; D019096:Vitronectin; C037405:heparin-sepharose; D015844:Heparin Cofactor II; D006493:Heparin; D012685:Sepharose; D010960:Plasminogen Activators; D013917:Thrombin