Size-dependent diffusion of membrane inclusions

¹ German Cancer Research Center
² German Cancer Research Center (DKFZ)

^* To whom correspondence should be addressed. E-mail: m.weiss{at}dkfz.de.

Submitted on April 12, 2006
Revised on May 14, 2006
Accepted on 9 June 2006

	Abstract

Experimentally determined diffusion constants are often used to elucidate the size and oligomeric state of membrane proteins and domains. This approach critically relies on the knowledge of the size-dependence of diffusion. We have used mesoscopic simulations to thoroughly quantitate the size-dependent diffusion properties of membrane inclusions. For small radii R, we find that the lateral diffusion coefficient D is well described by the Saffman-Delbruck relation which predicts a logarithmic decrease of D with R. However, beyond a critical radius R_c h_m/(2_c) (h: bilayer thickness, _m/c: viscosity of the membrane/surrounding solvent) we observe significant deviations and the emergence of an asymptotic scaling D~1/R². The latter originates from the asymptotic hydrodynamics and the inclusion's internal degrees of freedom that become particularly relevant on short time scales. In contrast to the lateral diffusion, the size dependence of the rotational diffusion constant D_r follows the predicted hydrodynamic scaling D_r~1/R² over the entire range of sizes studied here.

Key Words: diffusion, membrane, membrane inclusion, mesoscopic simulation