Double Bilayers and Transmembrane Gradients: A Molecular Dynamics Study of a Highly Charged Peptide

¹ Johns Hopkins University, School of Medicine

^* To whom correspondence should be addressed. E-mail: twoolf{at}jhmi.edu.

Submitted on March 24, 2008
Revised on April 16, 2008
Accepted on 27 May 2008

	Abstract

The position and extent of movement of a charged peptide within a membrane bilayer provides much controversy. In our study, we have examined the nature of the highly charged helix-turn-helix motif (S3b and S4) to address how a highly charged peptide is stabilized within a bilayer in the presence of various transmembrane electrical potentials. Our double-bilayer simulation results show how the variation of the salt concentrations between the inner and outer bath establishes a transmembrane potential. Our results also show that important features of the peptide affected by changes in electrical potential are the center of mass depth, the swivel/kink degrees of conformation, and the hydrogen-bonding patterns. As the voltage gradient across the bilayer increased, the center of mass of the peptide shifted in a direction towards the outer bath. The peptide also has a higher percent helical content and the swivel/kink conformation is more rigid for non-polarized systems where no voltage drop occurred between salt baths. Our results also provide some suggestions for how this domain may be affected by environmental changes as part of the voltage sensor in a K-channel.

Key Words: S4 segment, free energy calculations, gating, protein:lipid interactions