Stand up and take hold

Integrin is being examined inside and out. Olga Vinogradaova, Edward Plow, Jun Qin, and colleagues (The Cleveland Clinic Foundation, Cleveland, OH) have focused on its intracellular portion, and Junichi Takagi, Timothy Springer, and colleagues (Harvard Medical School, Boston, MA) have examined extracellular domains. Their combined efforts reveal a jackknife-like opening of the stimulated protein.

Changes in integrin structure in response to cellular signals regulate its binding to extracellular matrix (ECM) proteins like fibrinogen during processes such as platelet aggregation. Integrin is composed of α and β subunits, each of which is a transmembrane protein with a short cytoplasmic tail and several large extracellular domains. The binding sites for extracellular ligands lie far from the transmembrane domain, so how an intracellular signal is transmitted through so many...