@article {548811, title = {Modulation of integrin activation by an entropic spring in the β-knee.}, journal = {J Biol Chem.}, volume = {285}, number = {43}, year = {2010}, pages = {32954-66}, abstract = {We show that the length of a loop in the β-knee, between the first and second cysteines (C1-C2) in integrin EGF-like (I-EGF) domain 2, modulates integrin activation. Three independent sets of mutants, including swaps among different integrin β-subunits, show that C1-C2 loop lengths of 12 and longer favor the low affinity state and masking of ligand-induced binding site (LIBS) epitopes. Shortening length from 12 to 4 residues progressively increases ligand binding and LIBS epitope exposure. Compared with length, the loop sequence had a smaller effect, which was ascribable to stabilizing loop conformation, and not interactions with the α-subunit. The data together with structural calculations support the concept that the C1-C2 loop is an entropic spring and an emerging theme that disordered regions can regulate allostery. Diversity in the length of this loop may have evolved among integrin β-subunits to adjust the equilibrium between the bent and extended conformations at different set points.}, author = {Smagghe, B. and Huang, P. and Ban, Y-E. and Baker, D. and Springer, TA.} }