Temperature dependence of the far infrared signature of internal hydrogen bonds in proteins as probed for integrins

The basic motions and the conformational flexibility of a protein have a strong impact on its molecular recognition properties and ultimately on its function. In the far infrared (or THz) spectral range the breathing of the hydrogen bonds can be monitored, providing essential information on local dynamics and mechanism. The use of this spectral range is rapidly evolving and a number of IR synchrotron beamlines are available for this research. Here we present a study on the I-domain of the integrin LFA-1, an allosteric receptor that transmits signals across the plasma membrane in a bidirectional way. The I-domain contains the principal binding site for extracellular ligands and thus crucial for the signaling and the integrin-mediated cell adhesion. We measured the temperature dependence of the conformational dynamics of the I-domain bound to four different divalent metal ions (Mg ²⁺, Ca ²⁺, Mn ²⁺ and Fe ²⁺) in the range 10-300 K. The H-bonding vibrations show distinct temperature dependences for the different samples.