Integrins are α/β heterodimeric cell surface receptors devoid of enzymatic activity. Signal transduction therefore requires the association of cytosolic and cytoskeletal proteins with the integrin subunit intracellular regions. This association is initiated upon ligand binding to the integrin receptor and includes clustering of the integrins and recruitment of focal adhesion-associated proteins. Whether integrin clustering is solely dependent on ligand binding to the integrin extracellular parts or involves also interactions between the intracellular tails of integrins is so far unknown. To investigate intracellular events in integrin clustering, we have used peptides corresponding to the integrin β1 cytoplasmic region. Loading of cells with the peptides results in a decreased cell adhesion and in an inhibition of cell spreading in agreement with the previously reported dominant negative effect of the β1 integrin cytoplasmic tail on integrin clustering. Direct protein-protein interaction studies by surface plasmon resonance demonstrate that integrin β1 cytoplasmic peptides self-associate in contrast to integrin β3 cytoplasmic tails. Size exclusion chromatography and SDS-PAGE analysis of the peptides further show that the integrin β1 cytoplasmic parts form oligomers and that they assume a helical conformation to the extent of about 13% and that this fraction is increased upon aggregation. Thus self-association of the integrin β1 subunit cytoplasmic regions may be central to β1 integrin clustering.
- Focal complexes
- Protein-protein interaction