Potentiation of wheat germ agglutinin aggregation of platelets by von Willebrand protein and by a 116,000 molecular weight tryptic fragment.
This study compares selected properties of purified tryptic fragments of human von Willebrand (vW) protein in order to better understand how the M(r) 116,000 fragment retains activity in ristocetin-induced platelet agglutination. Wheat germ agglutinin (WGA) aggregation of platelet-rich plasma was potentiated by preincubation of WGA with intact vW protein and with the M(r) 116,000 moiety, but not by the smaller (M(r) 45,000) or larger (M(r) 220-250,000) tryptic fragments. Since all of the fragments bound to WGA, the unique potentiating effect of the M(r) 116,000 fragment on platelet aggregation could not be explained by differential ability to form a complex with this lectin. No clearcut difference in binding of tryptic fragments to platelets in the presence of ristocetin was found, and all of the tryptic fragments had approximately equal content of carbohydrate, as reflected by periodic acid-Schiff staining and binding to the lectin Ricinus communis type II. The M(r) 116,000 fragment contains a subunit polypeptide chain of M(r) 73,000 that is lacking from both larger and smaller fragments in the tryptic digest. This chain may possess critical features that mimic the optimal structure of vW protein that forms intercellular bridges and promotes agonist stimulation by WGA via membrane receptors.
Martin
S E
SE
Hematology Unit, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
Francis
C W
CW
Marder
V J
VJ
D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects*; D011487:Protein Conformation; D021122:Protein Subunits; D012310:Ristocetin / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism*; D014909:Wheat Germ Agglutinins / Q000378:metabolism / Q000494:pharmacology*; D014841:von Willebrand Factor / Q000737:chemistry / Q000378:metabolism*
D010446:Peptide Fragments; D021122:Protein Subunits; D014909:Wheat Germ Agglutinins; D014841:von Willebrand Factor; D012310:Ristocetin; D014357:Trypsin