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A mutation in the integrin alphaIIb subunit that selectively inhibits alphaIIb beta3 receptor function
Kim B Perkins1, Joseph C Loftus
1Mayo Clinic Scottsdale, 13400 E. Shea Boulevard, Scottsdale, Arizona 85259, USA.
Thrombosis and Haemostasis
|November 5, 2003
Summary
A key residue in alpha(IIb)beta(3) integrin, Serine 96, is crucial for binding fibrinogen and other ligands. This discovery offers insights into platelet function and potential therapeutic targets for thrombosis.
Area of Science:
- Integrin biology
- Molecular cell biology
- Biochemistry
Background:
- Integrins, such as alpha(IIb)beta(3), are vital cell surface receptors involved in various physiological and pathological processes.
- Alpha(IIb)beta(3) is a platelet-specific receptor essential for thrombosis and hemostasis, mediating fibrinogen binding.
- Understanding ligand recognition by alpha(IIb)beta(3) is critical for developing strategies to modulate platelet activity.
Purpose of the Study:
- To identify specific amino acid residues within the alpha(IIb) subunit that are critical for alpha(IIb)beta(3) ligand binding.
- To elucidate the structural and functional significance of identified residues in receptor-ligand interactions.
Main Methods:
- Random mutagenesis of cells expressing a constitutively active alpha(IIb)beta(3) variant.
- Selection of mutants with impaired ligand binding function.
- Biochemical assays to assess binding to ligand mimetics (PAC1 antibody) and fibrinogen.
- Analysis of RGD-dependent binding interactions.
Main Results:
- A single amino acid substitution (Ser96-->Leu) in alpha(IIb) abolished ligand binding to alpha(IIb)beta(3).
- This mutant receptor failed to bind PAC1 antibody, fibrinogen, or an RGD affinity matrix.
- Substitution of analogous serine residues in other integrin repeats also impaired alpha(IIb)beta(3) ligand binding.
- Mutations at analogous positions in alpha(v) or alpha(4) subunits did not disrupt ligand binding in alpha(v)beta(3) or alpha(4)beta(1) integrins.
Conclusions:
- Alpha(IIb) residue 96 (Ser96) plays a unique and critical role in alpha(IIb)beta(3) ligand binding.
- The location of Ser96 within the beta-propeller fold suggests a specific structural or mechanistic function in receptor activation or ligand interface.
- These findings highlight a potential unique feature of alpha(IIb)beta(3) compared to other integrins, offering insights for targeted therapeutic interventions.