(469f) Characterizing Mechanisms for the Translocation of Charged Peptides across Lipid Bilayers with Enhanced Sampling Simulations

Authors: 
Patel, S. J., University of Wisconsin-Madison
Van Lehn, R. C., University of Wisconsin-Madison
The hydrophobic core of the cell membrane is considered impermeable to charged molecules because of the large free energy barrier and corresponding long timescale (~hours) for charge translocation. Contradicting this view, a variety of water-soluble peptides are known to translocate charged groups across the cell membrane on a surprisingly rapid timescale, on the order of few seconds at least for some peptides. In this work, we study the bilayer translocation of a peptide with charged flanking loops and a central aspartate residue with varying protonation state. We utilize all-atom Temperature Accelerated Molecular Dynamics (TAMD) simulations to predict the likelihood of peptide translocation without predefining specific translocation pathway. We show that membrane-exposed charged residues accelerate the translocation of charged peptide loops by stabilizing water defects, enabling the “self-catalysis” of translocation. We further demonstrate that this approach can identify multiple flipping pathways without specifying them a priori. These detailed molecular-level insights of peptide translocation pathways may be valuable for designing small cationic peptides for applications in gene and drug delivery. Moreover, the methodology and findings discussed here can generalize to more complex behaviors, such as the large-scale conformational rearrangements of integral membrane proteins.