Sulfatides partition disabled-2 in response to platelet activation.

Sulfatides partition disabled-2 in response to platelet activation.

Blog Article

BACKGROUND:Platelets contact each other at the site of vascular injury to stop bleeding.One negative regulator of platelet aggregation is Disabled-2 (Dab2), which is released to the extracellular surface upon platelet activation.Dab2 inhibits platelet aggregation through its phosphotyrosine-binding (PTB) domain by competing with fibrinogen for alphaIIbbeta3 integrin receptor binding by an unknown mechanism.METHODOLOGY/PRINCIPAL FINDINGS:Using protein-lipid overlay and liposome-binding assays, we identified that the N-terminal region of Dab2, including its Brake Pump Relocation Bracket PTB domain (N-PTB), specifically interacts with sulfatides.Moreover, we determined that such interaction is mediated by two conserved basic motifs with a dissociation constant (K(d)) of 0.

6 microM as estimated by surface plasmon resonance (SPR) analysis.In addition, liposome-binding assays combined with mass spectroscopy studies revealed that thrombin, a strong platelet agonist, cleaved N-PTB at a site located between the basic motifs, a region that becomes protected from thrombin cleavage when bound to sulfatides.Sulfatides on the platelet surface interact with coagulation proteins, playing a major role in haemostasis.Our results show that sulfatides recruit N-PTB to the platelet surface, sequestering it from integrin receptor binding during platelet activation.This is a transient recruitment that follows N-PTB internalization by an actin-dependent process.

CONCLUSIONS/SIGNIFICANCE:Our experimental data support a model where two pools of Dab2 co-exist at the platelet surface, in both Cutting Saddle sulfatide- and integrin receptor-bound states, and their balance controls the extent of the clotting response.