aheadofpub,
Multiple Diffusion Mechanisms Due to Nanostructuring in Crowded Environments.
(October 2006)
DOI: 10.1529/biophysj.106.090498
Abstract
One of the key questions regarding intracellular diffusion is how
the environment affects molecular mobility. Mostly, intracellular
diffusion has been described as hindered, and the physical reasons
for this behavior are: immobile barriers, molecular crowding, and
binding interactions with immobile or mobile molecules. Using results
from multi-photon fluorescence correlation spectroscopy, we describe
how immobile barriers and crowding agents affect translational mobility.
To study the hindrance produced by immobile barriers, we used sol-gels
(silica nanostructures) that consist of a continuous solid phase
and aqueous phase in which fluorescently tagged molecules diffuse.
In the case of molecular crowding, translational mobility was assessed
in increasing concentrations of 500 kDa dextran solutions. Diffusion
of fluorescent tracers in both sol-gels and dextran solutions shows
clear evidence of anomalous subdiffusion. In addition, data from
the autocorrelation function was analyzed using the maximum entropy
method as adapted to fluorescence correlation spectroscopy data and
compared with the standard model that incorporates anomalous diffusion.
The maximum entropy method revealed evidence of different diffusion
mechanisms that had not been revealed using the anomalous diffusion
model. These mechanisms likely correspond to nanostructuring in crowded
environments and to the relative dimensions of the crowding agent
with respect to the tracer molecule. Analysis with the maximum entropy
method also revealed information about the degree of heterogeneity
in the environment as reported by the behavior of diffusive molecules.
