Transient anomalous subdiffusion: effects of specific and nonspecific probe binding with actin gels

J Phys Chem B. 2010 Jan 21;114(2):959-72. doi: 10.1021/jp9072153.

Abstract

When signaling molecules diffuse through the cytosol, they encounter a wide variety of obstacles that hinder their mobility in space and time. Some of those factors include, but are not limited to, interactions with mobile and immobile targets or obstacles. Besides finding a crowded environment inside the cell, macromolecules assemble into molecular complexes that drive specific biological functions adding additional complexity to their diffusion. Thus, simple models of diffusion often fail to explain mobility through the cell interior, and new approaches are needed. Here we used fluorescent correlation spectroscopy to measure diffusion of three molecules of similar size with different surface properties diffusing in actin gels. The fluorescent probes were (a) quantum dots, (b) yellow-green fluorescent spheres, and (c) the beta isoform of Ca(2+) calmodulin-dependent protein kinase II tagged with green fluorescent protein. We compared various models for fitting the autocorrelation function (ACF) including single component, two-component, and anomalous diffusion. The two-component and anomalous diffusion models were superior and were largely indistinguishable based on a goodness of fit criteria. To better resolve differences between these two models, we modified the ACF to observe temporal variations in diffusion. We found in both simulated and experimental data a transient anomalous subdiffusion between two freely diffusing regimes produced by binding interactions of the diffusive tracers with actin gels.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / chemistry*
  • Actins / isolation & purification
  • Animals
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / chemistry
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / isolation & purification
  • Diffusion
  • Fluorescent Dyes / chemistry*
  • Gels / chemistry*
  • Green Fluorescent Proteins / chemistry
  • Green Fluorescent Proteins / isolation & purification
  • Muscle, Skeletal / chemistry
  • Quantum Dots
  • Rabbits
  • Spectrometry, Fluorescence*

Substances

  • Actins
  • Fluorescent Dyes
  • Gels
  • Green Fluorescent Proteins
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2