Water diffusion through a membrane protein channel: A first passage time approach

Water diffusion through a membrane protein channel: A first passage time approach

Van Hijkoop, V.J.
Dammers, A.J.
Malek, K.
Coppens, M.O.

Applied Sciences

DelftChemTech

2007-08-28

Water diffusion through OmpF, a porin in the outer membrane of Escherichia coli, is studied by molecular dynamics simulation. A first passage time approach allows characterizing the diffusive properties of a well-defined region of this channel. A carbon nanotube, which is considerably more homogeneous, serves as a model to validate the methodology. Here we find, in addition to the expected regular behavior, a gradient of the diffusion coefficient at the channel ends, witness of the transition from confinement in the channel to bulk behavior in the connected reservoirs. Moreover, we observe the effect of a kinetic boundary layer, which is the counterpart of the initial ballistic regime in a mean square displacement analysis. The overall diffusive behavior of water in OmpF shows remarkable similarity with that in a homogeneous channel. However, a small fraction of the water molecules appears to be trapped by the protein wall for considerable lengths of time. The distribution of trapping times exhibits a broad power law distribution ?(?) ? ???2.4, up to ? = 10?ns, a bound set by the length of the simulation run. We discuss the effect of this distribution on the dynamic properties of water in OmpF in terms of incomplete sampling of phase space.

biomembranes
cellular biophysics
diffusion
molecular dynamics method
proteins
water

http://resolver.tudelft.nl/uuid:fcfe25a8-98c2-413e-ae56-c94c723a4fb4

https://doi.org/10.1063/1.2761897

American Institute of Physics

0021-9606

http://link.aip.org/link/JCPSA6/v127/i8/p085101/s1

Journal of Chemical Physics, 127 (8), 2007

Institutional Repository

journal article

(c) 2007 Van Hijkoop, V.J.; Dammers, A.J.; Malek, K.; Coppens, M.O.; American Institute of Physics