Torsional properties of proteins

Master's project Alexander van Reenen

We are investigating the properties of protein complexes under a mechanical torque. The aim is to quantify the molecular complex and its bond strength for future multifunctional biosensors.

A well-controlled torque is applied to the molecules using a superparamagnetic bead in a rotating magnetic field (Janssen et al, Bios. Bioel. 2009). The molecular model system is the protein G - IgG complex, schematically represented in the top figure.

The magnetic torque causes the superparamagnetic bead to rotate. The applied torque is opposed by the torque due to hydrodynamic drag and by the torque of the molecular system. The rotation of the beads (diameter 3 micrometer) is visualized by tagging the beads with fluorescent particles (diameter 200 nm). The bottom figure shows a microscope image of superparamagnetic beads that are labeled by fluorescent nanoparticles