Resolving mechanisms of protein dynamics and organization at the cell membrane in single molecule detail


Signaling complexes are out-of-equilibrium, heterogeneous multi-molecular structures and sites for intracellular signal transduction. Although they play a crucial role in cellular activation, current research techniques have been unable to resolve their structure and formation mechanisms in
intact cells. I will briefly review recent advancements in far-field super-resolution optical microscopy and present a multi-color Single Molecule Localization Microscopy (SMLM) approach for imaging multiple types of single molecules in fixed and live cells, with resolution down to ~20nm. I will further describe a statistical framework to determine the nanoscale organization and cooperativity of molecular interactions in signaling complexes. Using these techniques we observed that signaling complexes that determine immune (T) cell activation showed surprising patterns of dynamic nanoscale organization and a hierarchical network of cooperative interactions between the constituent molecules.

In the second part of my talk, I will describe our study of protein mobility at the plasma-membrane using single particle tracking (SPT). I will further present a methodological approach to resolve mixed subdiffusion mechanisms acting simultaneously on polydispersed samples and complex media such as cell membranes. Using these tools, we find that protein mobility of a short trans-membrane protein is highly heterogeneous, subdiffusive and ergodic-like. Individual trajectories can be broken into distinct mobility states having distinct underlying subdiffusion mechanisms. These mechanisms include viscoelasticity, fractality, and confinement.


Taken together, our results extend our understanding of protein dynamics, organization and function within the complex medium of the cell.