# Platelet Integrin Structure and Function

> **NIH NIH P01** · UNIVERSITY OF PENNSYLVANIA · 2022 · $761,784

## Abstract

Project 2: Summary
Platelet αIIbβ3 has been considered the prototypic integrin whose quintessential feature is its
nearly instantaneous conversion from an inactive bent conformation on circulating platelets to an
extended ligand binding conformation following vascular trauma. This global reorganization is
initiated by platelet agonist-stimulated biochemical reactions that disrupt an intramolecular clasp
composed of portions of the αIIb and β3 cytosolic, transmembrane, and extracellular stalk
domains. Recent work suggests that αIIbβ3 is not representative of all integrins and that various
integrins differ in the stringency of their regulation. Unlike αIIbβ3, some integrins may be
constitutively active. Project 2 addresses topics related to the protein-protein interactions that
maintain integrins in their basal states, intra-molecular interactions in Specific Aim 1 and inter-
molecular interactions in Specific Aim 2. In Specific Aim 1, intramolecular constraints located in
the interface between the αIIb and β3 extracellular stalks will be identified using a novel structural
bioinformatics method to predict interacting interfacial “hot spots”. The relative importance of the
predicted hot spots will then be determined by expressing hot spot mutants in CHO cells and in
iPSC-derived human megakaryocytes produced in collaboration with Project 4. This experimental
approach will then be used to compare αIIbβ3 to the integrins αvβ3, α2β1, and αvβ8 and in
collaboration with Project 1, to characterize the interaction between the PH and BEACH domains
of Nbeal2 in studies designed to understand the pathogenesis of α granule defect in the gray
platelet syndrome. A second set of integrin constraints located in the transmembrane domain
interface will be studied based on preliminary data indicating that β3 uses different motifs to
interact with αIIb and αv. Novel computational methods will then be used to derive two-
dimensional kinetic parameters for these interactions in collaboration with Project 3. Lastly, we
will use high-resolution cryo-electron microscopy to correlate our computational and experimental
results with the global conformation of full-length integrins. Specific Aim 2 will the identify and
quantitively evaluate the protein-protein interactions responsible for αIIbβ3-mediated fibrin clot
contraction. The studies are based on the observation that agonist stimulation causes platelet
calpain activation and the degradation of platelet cytosolic proteins, in particular the proteins talin
and vinculin that link αIIbβ3 to the actin cytoskeleton. Proposed studies will test the hypothesis
that talin cleavage by calpain enables vinculin binding, thereby generating sufficient traction force
to contract αIIbβ3-bound fibrin clots. This hypothesis will also be tested in vivo using mouse
thrombosis models and calpain-deficient mice in collaboration with Project 3.

## Key facts

- **NIH application ID:** 10434810
- **Project number:** 5P01HL146373-03
- **Recipient organization:** UNIVERSITY OF PENNSYLVANIA
- **Principal Investigator:** Joel S. Bennett
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $761,784
- **Award type:** 5
- **Project period:** 2020-05-10 → 2025-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10434810

## Citation

> US National Institutes of Health, RePORTER application 10434810, Platelet Integrin Structure and Function (5P01HL146373-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10434810. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*