Actuation spectroscopy as a new label-free tool to study protein properties in real time

Proteins carry out all functions in living cells, from division, metabolism and transport to programmed cell death. Understanding how protein structure and movements relate to their function is key to advancing biology and medicine.

A recent breakthrough, interferometric scattering (iSCAT) microscopy, allows us to observe single protein molecules without using fluorescent labels or chemical tethers.

This innovation enables label-free protein studies but currently cannot detect changes in protein shape and structure.With ProAct, I aim to enhance iSCAT microscopy by introducing a new way to detect protein conformational changes. The key idea is to measure how a protein responds to an uneven electric field.

When a protein moves in this field, it experiences a dielectrophoretic force that depends on its dipole moment, which is influenced by the protein's structure, conformational dynamics, and interactions.

Within the ProAct project, we will focus on quantifying this dielectrophoresis force, as it provides a unique experimental approach to accessing protein dipole momentspreviously only computable.

By using nanoelectrodes to create this inhomogeneous electric field, we can register the protein motion with iSCAT and discern the protein properties from its trajectory.

This combination represents a completely new approach to studying protein behavior without labels, as it enriches the palette of protein properties measurable at the single-molecule level.I expect that the ProAct method will make it much easier to study how proteins move and interact with other molecules.

It could also change how we think about proteins in electric fields by helping to understand the role of the dipole moment in protein properties. ProAct pushes iSCAT microscopy into exciting new territory for observing molecular dynamics.