# Platelet Integrin AlphaIIbBeta3 Structure, Activation, and Ligand Binding: Fibrinogen, Fibrin, D-dimer, and von Willebrand Factor

> **NIH NIH R01** · ROCKEFELLER UNIVERSITY · 2024 · $743,861

## Abstract

Project Summary/Abstract
Platelets play a key role in both hemostasis and thrombosis and contribute to COVID-19 pathology. Platelet
αIIbβ3 is the paradigmatic integrin receptor and a validated drug target, with abciximab, developed under this
grant, the first FDA-approved αIIbβ3 antagonist. In the current grant period, we rationally designed and
synthesized novel αIIbβ3 and αVβ3 antagonists that lock the receptor in the inactive conformation, which may
confer therapeutic benefits. The αIIbβ3 antagonist (RUC-4; zalunfiban) is now in Phase 2 human studies for pre-
hospital therapy of heart attacks and the αVβ3 antagonists are being developed for pre-clinical testing. We also
began studying key gaps in our understanding of how αIIbβ3: 1. Binds its medically important ligands, including
fibrinogen, polymerizing fibrin, von Willebrand factor (vWf), and cross-linked fibrin. 2. Initiates clot retraction to
confer resistance to thrombolysis. 3. Transitions from its inactive to its active state. Thus, we studied the
interaction of αIIbβ3 with fragment D-dimer and used a novel functional assay to dissect the interaction of αIIbβ3
with polymerizing fibrin. In addition, we obtained high-resolution cryo-electron microscopy (EM) structures of
αIIbβ3 in complex with abciximab and with the activating monoclonal antibody (mAb) PT25-2, providing data on
each antibody’s mechanism of activation. We also initiated hydrogen-deuterium exchange-mass spectroscopy
(HDX) studies of αIIbβ3 to provide peptide-level dynamic structural information on ligand binding and receptor
activation to complement cryo-EM data. The new Specific Aims build on the PI’s long-standing collaborations
with Dr. Marta Filizola, an expert in computational methods, and Dr. Thomas Walz, an expert in cryo-EM.
 Specific Aim 1. A. To determine high-resolution cryo-EM structures of D-dimer and of αIIbβ3 in complex
with: 1) fibrinogen fragment D100 and fibrinogen γ-module; 2) vWf C4 domain; 3) D-dimer. B. To obtain peptide-
level solvent-exposed area data by HDX on αIIbβ3 alone and in complex with the ligands. C. To obtain
complementary structural and dynamics information from computer simulations to guide mutational analysis and
mAb production to validate the proposed mechanisms of binding, as well as to develop novel ligand-specific
small-molecule antagonists. Specific Aim 2. To utilize currently available and future cryo-EM data sets in concert
with computational and HDX data to define intermediate structures of the integrin leg domains along the αIIbβ3
activation pathway. Specific Aim 3. To utilize our novel functional polymerizing fibrin assays using platelets and
HEK293 cells expressing native and mutant forms of αIIbβ3, in concert with mAbs and small-molecule αIIbβ3
antagonists, to define the unique αIIbβ3 ligand-specific binding mechanisms and develop ligand-specific
inhibitors. A. To produce mAbs to D-dimer that inhibit platelet-fibrin, but not platelet-fibrinogen interactions. B.
To identify mu...

## Key facts

- **NIH application ID:** 10770429
- **Project number:** 5R01HL019278-48
- **Recipient organization:** ROCKEFELLER UNIVERSITY
- **Principal Investigator:** Barry Coller
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $743,861
- **Award type:** 5
- **Project period:** 1976-09-01 → 2026-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10770429

## Citation

> US National Institutes of Health, RePORTER application 10770429, Platelet Integrin AlphaIIbBeta3 Structure, Activation, and Ligand Binding: Fibrinogen, Fibrin, D-dimer, and von Willebrand Factor (5R01HL019278-48). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10770429. Licensed CC0.

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