Identification of integrin beta subunit mutations that alter affinity for extracellular matrix ligand

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Integrins are crucial cell surface receptors mediating cell adhesion.
• Regulation of integrin affinity is vital for diverse cellular processes.
• The Drosophila βPS integrin subunit is a key component of the PS integrin family.

Purpose of the Study:

• To investigate the functional consequences of over 50 mutations in the Drosophila βPS integrin subunit.
• To determine how these mutations affect ligand binding and integrin activation.
• To explore the role of specific domains and residues in integrin affinity regulation.

Main Methods:

• In situ analysis of over 50 Drosophila βPS integrin mutations.
• Assessment of ligand binding to soluble monovalent ligand TWOW-1.
• Site-directed mutagenesis of cytoplasmic domains.
• Genetic interaction studies with talin reduction.

Main Results:

• Few mutations reduced ligand binding; most activated the integrin heterodimer.
• Findings support the deadbolt hypothesis, implicating the β tail CD loop in I domain restraint.
• Mutations in cytoplasmic domains revealed distinct effects on ligand binding compared to αIIbβ3.
• A conserved cytoplasmic cysteine residue was identified as important for affinity regulation.

Conclusions:

• Integrin affinity is tightly regulated by molecular interactions throughout the integrin molecule.
• The deadbolt hypothesis provides a strong model for integrin inactivation.
• Cytoplasmic domains, including a conserved cysteine, play critical roles in integrin affinity modulation.
• Genetic interactions with talin offer insights into integrin function beyond simple affinity changes.