Abstract
Film bulk acoustic resonators (FBAR) are mass sensitive, label-free biosensors that allow monitoring of the interaction between biomolecules. In this paper we use the FBAR to measure the binding of calcium and the CaMKII peptide to calmodulin. Because the mass of the calcium is too small to be detected, the conformational change caused by the binding process is measured by monitoring the resonant frequency and the motional resistance of the FBAR. The resonant frequency is a measure for the amount of mass coupled to the sensor while the motional resistance is influenced by the viscoelastic properties of the adsorbent. The measured frequency shift during the calcium adsorptions was found to be strongly dependent on the surface concentration of the immobilized calmodulin, which indicates that the measured signal is significantly influenced by the amount of water inside the calmodulin layer. By plotting the measured motional resistance against the frequency shift, a mass adsorption can be distinguished from processes involving measurable conformational changes. With this method three serial processes were identified during the peptide binding. The results show that the FBAR is a promising technology for the label-free measurement of conformational changes.
Highlights
Many proteins undergo conformational changes upon the binding of a ligand
We show that the Film bulk acoustic resonators (FBAR) is highly sensitive to the conformational changes of calmodulin and that it is possible to distinguish between mass adsorption and conformational changes
In this paper we used the FBAR to monitor the conformational changes of calmodulin caused by calcium and peptide binding
Summary
Many proteins undergo conformational changes upon the binding of a ligand. Because typically only small parts of the proteins (the domains) are involved in a certain function even a small conformational change can cause significant changes in the protein’s functional activity. Controlling this activity e.g., of protein kinases is of interest in for example cancer therapy [1]. A wide range of technologies was employed to investigate the conformational changes of calmodulin. We use the FBAR to investigate the response of the resonant frequency and the motional resistance to the conformational changes of calmodulin on calcium and peptide binding. We show that the FBAR is highly sensitive to the conformational changes of calmodulin and that it is possible to distinguish between mass adsorption and conformational changes
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