MicroRNAs as Clinical Biomarkers and Therapeutic Tools in Perioperative Medicine

Integrins are alpha/beta heterodimers that interconvert between inactive and active states. In the active state the alpha/beta cytoplasmic domains recruit integrin-activating proteins and separate the transmembrane and cytoplasmic (TMcyto) domains (unclasped TMcyto). Conversely, in the inactive state the alpha/beta TMcyto domains bind integrin-inactivating proteins, resulting in the association of the TMcyto domains (clasped TMcyto). Here, we report the isolation of integrin cytoplasmic tail interactors using either lipid bicelle-incorporated integrin TMcyto domains (alpha 5, alpha M, alpha IIb, beta 1, beta 2 and beta 3 integrin TMcyto) or a clasped, lipid bicelle-incorporated alpha M beta 2 TMcyto. Among the proteins found to preferentially bind clasped rather than the isolated aM and beta 2 subunits was L-plastin (LCP1, also known as plastin-2), which binds to and maintains the inactive state of alpha M beta 2 integrin in vivo and thereby regulates leukocyte adhesion to integrin ligands under flow. Our findings offer a global view on cytoplasmic proteins interacting with different integrins and provide evidence for the existence of conformation-specific integrin interactors.