Probing protein-ligand bond characteristics with magnetic force microscopy

Postdoc project Asha Jacob

Protein interactions are important in nearly all biological processes. In this research we focus on characterizing the interactions of protein-ligand pairs by magnetic force microscopy.

Superparamagnetic particles are bound to a sensor surface by single protein-ligand pairs. The particles are imaged in an optical microscope and are placed in a magnetic field that induces a mechanical piconewton pulling force to the biological bonds between particles and surface. The time-dependent dissociation of particles is recorded, in a magnetic force that is either constant or increasing in time. The dissociation properties of the bound complex can be determined from a statistical analysis of particle dissociation as a function of time and applied force.

An intermolecular bond involves many atomic-scale interactions and 3D conformational changes in the binding pocket, accounting for its affinity. The dissociation path contains a multitude of energy barriers with intermediate energy-minimum states. The dissociation process over such a network of barriers depends on the applied force, so the force spectrum is unique to the unbinding pair. It is our aim to deduce from the spectrum the bond energy, the kinetic dissociation rate constant (koff), potential energy landscapes and structural parameters of the binding pocket.

The illustrations below sketch the dissociation of the streptavidin-biotin complex using magnetic force microscopy.