Time-Resolved SANS Reveals Pore-Forming Peptides Cause Rapid Lipid Reorganization

Published

January 15, 2021

Author(s)

Michael H. Nguyen, Mitchell DiPasquale, Brett W. Rickeard, Caesar G. Yip, Kaity N. Greco, Elizabeth Kelley, Drew Marquardt

Abstract

Cells depend on proper lipid transport and their precise distribution for vital cellular function. Disruption of such lipid organization can be initiated by external agents to cause cell death. Here, we investigate two antimicrobial pore-forming peptides, alamethicin and melittin, and their influence on lipid intervesicular exchange and transverse lipid diffusion (i.e. flip-flop) in model lipid vesicles. Small angle neutron scattering (SANS) and a strategic contrast matching scheme show the mixing of two isotopically distinct dimyristoylphosphocholine (DMPC) vesicle populations is promoted upon the addition of high (1/40) and low (1/150, 1/1000) peptide-to-lipid molar ratios. Parsing out the individual exchange and flip-flop rate constants revealed that alamethicin increases both DMPC flip-flop and exchange by approximately equal}2-fold when compared to methanol alone (the carrier solvent of the peptides). On the other hand, melittin affected DMPC flip-flop by a factor of 1 to 4, depending on concentration, but in general melittin is seen to be the better promoter of DMPC flip-flop at low concentrations. At low P/L ratios, melittin had little effect on DMPC exchange, but promoted lipid exchange at a high concentration. Thermodynamic parameters measured at high protein concen- trations (P/L = 1/40) yielded remarkable similarity in the values obtained for both peptides, indicating likeness in their mechanism of action despite differences in their proposed oligomeric pore structures. The entropic contributions to the free energy of activation became favorable upon peptide addition, while the enathlpy of activation remained the major barrier to lipid exchange and flip-flop.

Citation

New Journal of Chemistry

Volume

45

Issue

1

Pub Type

Journals

Keywords

SANS, lipid bilayer, flip-flop, pore-forming peptides

Citation

Nguyen, M. , DiPasquale, M. , Rickeard, B. , Yip, C. , Greco, K. , Kelley, E. and Marquardt, D. (2021), Time-Resolved SANS Reveals Pore-Forming Peptides Cause Rapid Lipid Reorganization, New Journal of Chemistry (Accessed October 8, 2024)