Electrostatic shape control of a charged molecular membrane from ribbon to scroll

Changrui Gao, Sumit Kewalramani, Dulce Maria Valencia, Honghao Li, Joseph M. McCourt, Monica Olvera De La Cruz*, Michael J. Bedzyk

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Bilayers of amphiphiles can organize into spherical vesicles, nanotubes, planar, undulating, and helical nanoribbons, and scroll-like cochleates. These bilayer-related architectures interconvert under suitable conditions. Here, a charged, chiral amphiphile (palmitoyllysine, C16-K1) is used to elucidate the pathway for planar nanoribbon to cochleate transition induced by salt (NaCl) concentration. In situ small- and wide-angle X-ray scattering (SAXS/WAXS), atomic force and cryogenic transmission electron microscopies (AFM and cryo-TEM) tracked these transformations over angstrom tomicrometer length scales. AFM reveals that the large length (L) to width (W) ratio nanoribbons (L/W > 10) convert to sheets (L/W → 1) before rolling into cochleates. A theoretical model based on electrostatic and surface energies shows that the nanoribbons convert to sheets via a first-order transition, at a critical Debye length, with 2 shallow minima of the order of thermal energy at L/W >> 1 and at L/W = 1. SAXS shows that interbilayer spacing (D) in the cochleates scales linearly with the Debye length, and ranges from 13 to 35 nm for NaCl concentrations from 100 to 5 mM. Theoretical arguments that include electrostatic and elastic energies explain the membrane rolling and the bilayer separation-Debye length relationship. These models suggest that the salt-induced ribbon to cochleate transition should be common to all charged bilayers possessing an intrinsic curvature, which in the present case originates from molecular chirality. Our studies show how electrostatic interactions can be tuned to attain and control cochleate structures, which have potential for encapsulating, and releasing macromolecules in a size-selective manner.

Original languageEnglish (US)
Pages (from-to)22030-22036
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number44
DOIs
StatePublished - Oct 29 2019

Keywords

  • Bilayer assembly
  • Cochleate
  • Electrostatics
  • Nanoribbon

ASJC Scopus subject areas

  • General

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