Arginine in membranes: connection between molecular dynamics simulations and translocon-mediated insertion experiments

Arginine in membranes: connection between molecular dynamics simulations and translocon-mediated insertion experiments
Schow et al. 2011 (G. von Heijne, White, Tobias) - Journal of Membrane Biology

• Experiments disagree with computation: MD simulations find energetic cost of inserting arginine is an order of magnitude greater than in molecular biology experiments
• MD simulation of guanidinium groups + helices containing Arg at different positions along the helix
• Can reduce discrepancy by considering free energy difference between arginine at the interface
• Suggests arg snorkels to the interface prevents it from residing in the bilayer center
• Challenge with MD - measures water-to-bilayer free energies whereas molecular biology measures partitioning from translocon to bilayer: what is the relationship here? 
• Might not be a thermodynamic cycle connecting the two paths (transolocon to bilayer vs. water to bilayer).