Membrane Dynamics

ANOMALOUS DIFFUSION

ANOMALOUS DIFFUSION AND ERGODICITY IN LIVE CELLS

The plasma membrane is a crowded environment where proteins and lipids move in the presence of mobile and immobile obstacles. Furthermore, membrane components often interact with cytosolic elements. We are exploring the dynamics of the voltage gated potassium channels Kv2.1and Kv1.4 and sodium channels Nav1.6, using single-molecule tracking. By dually labeling channels with GFP and quantum dots (QD), we gather information on both the individual molecule trajectories and the distribution of proteins in the plasma membrane as an ensemble.

ERGODICITY BREAKING

We analyze individual trajectories in terms of the time- and ensemble-averaged mean square displacements. Our results revealed that ion channels experience anomalous subdiffusion. We observe that the diffusion pattern is not ergodic in HEK cells and in hippocampal neurons, that is the ensemble and temporal distributions of displacements are different. Channel dynamics can be accurately modeled by the combination of a nonergodic continuous time random walk (CTRW) and an obstructed environment.

BULK-MEDIATED DIFFUSION

Diffusion at solid–liquid interfaces is crucial in many technological and biophysical processes. Although its behavior seems to be deceivingly simple, recent studies showing passive superdiffusive transport suggest that diffusion on surfaces may hide rich complexities. In particular, bulk-mediated diffusion occurs when molecules are transiently released from the surface to perform three-dimensional excursions into the liquid bulk. This phenomenon bears the dichotomy where a molecule always return to the surface but the mean jump length is infinite.

PUBLICATIONS

Weigel et al. “Ergodic and nonergodic processes coexist in the plasma membrane as observed by single molecule tracking”, PNAS 108, 6438 (2011)

Weigel et al. “Obstructed diffusion propagator analysis for single particle tracking”, Phys. Rev. E 85, 041924 (2012)

Krapf, “Mechanisms underlying anomalous diffusion in the plasma membrane”, Current Topics in Membranes 75, 167 (2015)

Campagnola et al., “Superdiffusive motion of membrane-targeting C2 domains”, Sci. Rep. 5, 17721 (2015)

Krapf et al. “Strange kinetics of bulk-mediated diffusion on lipid bilayers”, Phys. Chem. Chem. Phys. 18, 12633 (2016)

A. Weron et al. “Ergodicity breaking on the neuronal surface emerges from random switching between diffusive states”, Sci. Rep. 7, 5404 (2017)

 

COLLABORATORS

Krzysztof Burnecki, Olve Peersen, Grzegorz Sikora, Mike Tamkun, Aleksander Weron

THIS PROJECT IS SUPPORTED BY THE NATIONAL SCIENCE FOUNDATION THROUGH GRANT 1401432.

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