Physical Society Colloquium

Track me if you can: imaging the diffusion of single proteins in live cells

Claudiu Gradinaru

Department of Chemical & Physical Sciences
University of Toronto Mississauga

Proteins are the building blocks of life, and their chemical repertoire drives most biological processes. Some proteins have a stable 3D structure, but most of them are dynamic across a wide range of timescales. Such an example is the G protein-coupled receptors (GPCRs), which trigger highly specific cellular responses to environmental stimuli, such as photons, ions, peptides, neurotransmitters and odorants. They are implicated in many diseases and are the targets of more than one third of prescribed drugs.

In my lab, we capture the molecular choreography of biomolecules at the single-molecule level. By their very nature, single-molecule methods remove the averaging present other experiments and can reveal rare, possibly pathological states. Using a versatile home-built suite of single-molecule fluorescence microscopes, we can measure molecular distances, track the diffusion of proteins in the cell, count units in a supramolecular complex, and resolve structural dynamics from nanoseconds to seconds.

In my talk, I will illustrate the power of the single-molecule approach to delineate the diffusion patterns of GPCRs in live cells. This data-rich content allows us to take a closer look at how the cell environment, such as membrane fluidity, molecular crowding, confinement and interaction with lipids, impacts the GPCR signalling, and to test different ideas, such as the nature of basal signalling and the existence of signalling “hot spots”. The new insights will help define the molecular mechanisms of GPCR signalling in the native environment, understand its malfunction in related diseases, and help design better sensor assays and therapeutic drugs.