A beta 3 integrin mutation abolishes ligand binding and alters divalent cation-dependent conformation.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Integrin adhesion receptors mediate cell-cell and cell-extracellular matrix interactions.
• Ligand binding to integrins is critically dependent on divalent cations.
• The alpha IIb beta 3 integrin (platelet gpIIb/IIIa) is essential for platelet aggregation.

Purpose of the Study:

• To investigate the role of divalent cations in integrin ligand binding.
• To elucidate the molecular mechanism underlying the loss of ligand recognition in a mutant alpha IIb beta 3 integrin.
• To identify conserved residues involved in cation-dependent ligand binding across integrins.

Main Methods:

• Site-directed mutagenesis to create an Asp119----Tyr119 substitution in the beta 3 subunit of alpha IIb beta 3 integrin.
• Immunological assays to assess the interaction of the mutant integrin with divalent cations.
• Structural analysis of conserved residues in integrins and comparison with EF hand proteins.

Main Results:

• A mutant alpha IIb beta 3 integrin lacking ligand recognition exhibited altered interactions with divalent cations.
• The mutation responsible was a G-T transversion leading to an Asp119----Tyr119 substitution in the beta 3 subunit.
• The mutated residue is located near the bound ligand and within a conserved region rich in oxygenated residues.

Conclusions:

• The Asp119----Tyr119 substitution perturbs divalent cation binding, leading to loss of ligand recognition in alpha IIb beta 3 integrin.
• The conserved spacing and oxygenation of residues suggest a common mechanism of receptor-bound divalent cation interaction for ligand binding in all integrins.
• This finding provides insights into the fundamental principles of integrin function and cation-dependent adhesion.