2 – Isolation, Physicochemical Characterization, and Carbohydrate-Binding Specificity of Lectins

Crystal structure of a wheat germ agglutinin/glycophorin-sialoglycopeptide receptor complex. Structural basis for cooperative lectin-cell binding.

Crystallographic elucidation of the saccharide binding mode in wheat germ agglutinin and its biological significance.

The direct aggregation of platelets is thought to be an important event in the pathogenesis of viridans streptococcal endocarditis, but the mechanisms for platelet activation are unknown. We evaluated the processes by which two endocarditis-producing strains of viridans group streptococci activated human platelets in vitro, as measured by platelet cyclooxygenase activity, secretion, and aggregation. Addition of either streptococcal strain to platelets suspended in whole plasma resulted in a mean lag phase of 15.3 min, followed by platelet secretion and brisk aggregation. The lag phase duration was dependent on the platelet donor and appeared to be a function of direct platelet-bacterial interaction. Aggregation was partially inhibited by 20 muM [corrected] indomethacin and blocked completely by 1 mg of apyrase, an extracellular ADP hydrolase, per ml. Neither strain aggregated washed platelets suspended in Tyrode solution alone. However, both strains produced maximal aggregation when the platelet suspension was supplemented with 10% (final concentration) normal plasma. Studies with factor-deficient plasmas demonstrated that exogenous fibrinogen was required for aggregation. One or more additional plasma components were needed, which eluted with a molecular weight of 67,000 to 130,000 on gel permeation chromatography. These cofactors have not been described for other platelet agonists, which suggests that viridans streptococci may aggregate human platelets by a novel mechanism.

https://iai.asm.org/content/iai/55/8/1743.full.pdf

Mechanisms of platelet aggregation by viridans group streptococci.

A new protein, called alboaggregin-B (AL-B), has been isolated from Trimeresurus albolabris venom by ion-exchange chromatography. It agglutinated platelets without the need for Ca2+ or any other cofactor. The purified protein showed an apparent molecular mass on SDS-PAGE and gel filtration of about 23 kDa under nonreducing conditions. Ristocetin did not alter the binding of AL-B to platelets or affect AL-B-induced platelet agglutination. Agglutinating activity was not dependent on either proteolytic or lectin-like activity in AL-B. Binding analysis showed that AL-B bound to platelets with high affinity (Kd = 13.6 +/- 9.3 nM) at approximately 30,800 +/- 14,300 binding sites per platelet. AL-B inhibited the binding of labeled bovine von Willebrand factor (vWF) to platelets. Monoclonal antibodies against the 45-kDa N-terminal domain of platelet glycoprotein Ib inhibited the binding both of AL-B and of bovine vWF to platelets, and also inhibited platelet agglutination induced by AL-B and bovine vWF. Specific removal of the N-terminal domain of GPIb by treatment of the platelets with elastase or Serratia marcescens protease reduced the binding of labeled AL-B and bovine vWF to platelets and blocked platelet agglutination caused by both agonists. Monoclonal antibodies to glycoprotein IIb/IIIa, to bovine vWF, and to bovine serum albumin did not show any effect on the binding of AL-B to platelets. Our results indicate that the binding domain for AL-B on platelet GPIb is close to or identical with the one for vWF. This new protein may be a very useful tool for studying the interaction between platelets and vWF.

Alboaggregin-B: a new platelet agonist that binds to platelet membrane glycoprotein Ib.

Role of surface sialic acid in the interaction of wheat germ agglutinin with human platelets

Inhibition of Thrombin-Induced Platelet Aggregation by a Derivative of Wheat Germ Agglutinin. Evidence for a Physiologic Receptor of Thrombin in Human Platelets

Nancy G. Fossett

Papers

Role of surface sialic acid in the interaction of wheat germ agglutinin with human platelets

Inhibition of Thrombin-Induced Platelet Aggregation by a Derivative of Wheat Germ Agglutinin. Evidence for a Physiologic Receptor of Thrombin in Human Platelets

Evidence for multiple mechanisms of interaction between wheat germ agglutinin and human platelets.

Interaction of lentil lectin with human platelets. Evidence against glycoprotein II as aggregation mediator

Induction of serotonin secretion by cross-linking of surface receptors of a derivative of wheat germ agglutinin on human platelets.