Effect of the ionic strength and pH on the equilibrium structure of a neurofilament brush

¹ Wageningen University
² Institute of Macromolecular Compounds

^* To whom correspondence should be addressed. E-mail: frans.leermakers{at}wur.nl.

Submitted on January 17, 2007
Revised on March 7, 2007
Accepted on 9 April 2007

	Abstract

Using the numerical model of Scheutjens and Fleer, we investigated, on a self-consistent field level, the equilibrium structure of the neurofilament brush formed by projection domains of the constituent NF-H, NF-M and NF-L proteins. The phosphorylation of such a brush is a major regulatory process which triggers the relocation of the H tails from the NF core to the brush periphery. We explore how the pH and the ionic strength affect the re-arrangements in the NF brush structure upon phosphorylation. We demonstrate that the translocation of H tails in an individual NF occurs as a sharp cooperative transition below and up to the physiological salt concentration. Regularities of this process are reminiscent of the collapse-to-stretching transition in a cylindrical polyelectrolyte brush in a poor solvent. The effect of pH at physiological ionic strength is noticeable only in the acidic range and is more pronounced for a dephosphorylated NF.

Key Words: coarse grained model, neurofilament, phosphorilation of KSP repeats, physiological conditions, self-consistent field model, translocation H-projection domain

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