PB0375 - Deciphering the TLT-1 Fibrinogen ligand interaction.

Background: The platelet integrin αIIbβ3’s interaction with the plasma clotting fibrinogen protein plays a central role in thrombosis and hemostasis. Upon activation, platelets release TREM-Like Transcript-1 (TLT-1) from their a-granules onto their surface. Early studies have demonstrated that fibrinogen is a ligand for TLT-1. TLT-1 binding fibrinogen was a surprising discovery since αIIbβ3, the most abundant platelet receptor, also binds fibrinogen and facilitates platelet aggregation. It is difficult to understand why platelets have two fibrinogen binding receptors. Very little is known about the TLT-1-ffibrinogen interaction

Aims: Delineate the TLT-1 - Fibrinogen molecular interaction.

Methods: To develop a binding assay using an Octet Qke Bio-layer Interferometry (BLI) to delineate the molecular interaction between TLT-1 and fibrinogen and use mass spectrometry to identify specific regions of fibrinogen that interact with TLT-1.

Results: We first used BLI to demonstrate the TLT-1 Fibrinogen interaction. Figure 1 illustrates a strong association with no dissociation, suggesting a strong interaction between the TLT-1 and fibrinogen. To localize the exact binding sites for this molecular interaction, we digested fibrinogen using trypsin and carried out an immunoprecipitation (IP) followed by Liquid Chromatography-Mass Spectrometry (LC-MS/MS). We isolated and identified four potential peptides and are currently using the BLI to identify which of these regions are critical for binding TLT-1. We are also identifying the regions of TLT-1 that interact with fibrinogen. This poster will detail the current state of these studies.

Conclusion(s): The TLT-1/fibrinogen interaction has an equilibrium dissociation constant (KD) of 3.02 ± 0.20 nM. This interaction may play a larger role in hemostasis and inflammation that previously thought.