Integrin α1 Has a Long Helix, Extending from the Transmembrane Region to the Cytoplasmic Tail in Detergent Micelles

Integrin proteins are very important adhesion receptors that mediate cell-cell and cell-extracellular matrix interactions. They play essential roles in cell signaling and the regulation of cellular shape, motility, and the cell cycle. Here, the transmembrane and cytoplasmic (TMC) domains of integrin alpha 1 and beta 1 were over-expressed and purified in detergent micelles. The structure and backbone relaxations of alpha 1-TMC in LDAO micelles were determined and analyzed using solution NMR. A long helix, extending from the transmembrane region to the cytoplasmic tail, was observed in alpha 1-TMC. Structural comparisons of alpha 1-TMC with reported alpha IIb-TMC domains indicated different conformations in the transmembrane regions and cytoplasmic tails. An NMR titration experiment indicated weak interactions between alpha 1-TMC and beta 1-TMC through several alpha 1-TMC residues located at its N-terminal juxta-transmembrane region and C-terminal extended helix region.