Chemists in Canada have demonstrated the potential of acoustic waves in the study of protein activity. Michael Thompson and colleagues at the University of Toronto used a technique called acoustic shear wave propagation to detect conformational changes in proteins attached to surfaces.

Thompson's group concentrated on the small protein calmodulin - which has a well-characterised role in calcium-mediated cell signalling. The group anchored the protein onto the surface of a sensor chip and bombarded the chip with high-frequency acoustic waves. Biochemical events on the chip surface caused changes in wave properties that were monitored with time.

The activity of calmodulin depends on its binding with calcium (Ca²⁺) ions. A reversible interaction with Ca²⁺ ions makes the protein change from a closed, unbound state to an open, calcium-bound state. For the chip-bound protein this causes the chip to thicken and decreases the resonant frequency of the acoustic device. By measuring the resonant frequency the extent of calcium binding can be monitored. 

This is 'the first semi-quantitative detection of a protein conformational shift using an acoustic wave device,' said Thompson. This label-free biosensor methodology can be used to follow protein behaviour in simulated natural environments and has potential for miniaturisation and lab on a chip applications, he said.

Michael J Spencelayh