(618h) Monitoring of Conformational Change of a Calcium Binding Protein S100A5 Using QCM-D Sensor

Detecting conformational change of protein-protein binding is important in understanding their physiological functions.   Calcium dependent proteins undergo various structural rearrangements during binding with various binding moieties.   Such conformational change has been measured by NMR, AFM, or calorimetric method.  We demonstrate QCM-D characterization of conformational shift in calcium-dependent S100A5 protein  for binding to calcium, calmodulin (CaM), olfactory marker protein (OMP), and in its dimerization.   Simultaneous measurement of frequency and dissipation change of the QCM-D sensor enables one to characterize film thickness and flexibility upon bindings. His-tagged recombinant S100A5 was immobilized on to the gold QCM surface via NTA-Ni+ and binding moieties were applied.  Binding of calcium caused releasing of entrapped water making the thickness of S100A5 layer decrease.  Dimerization with non-his tagged recombinant S100A5 caused increased thickness at affinity of 3.7 ± 2 uM.   Binding to CaM and OMP caused decreased adlayer thickness with unique characteristics as demonstrated by changes in dissipation vs. frequency plot.   The result demonstrated QCM-D sensor could be employed  as an effective and simple way to detect diverse binding characteristics of protein conformational changes.