Phosphate-Mediated Arginine Insertion into Lipid Membranes and Pore Formation by a Cationic Membrane Peptide from Solid-State NMR

Ming Tang,† Alan J. Waring,‡ and Mei Hong*†
Contribution from the Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Medicine, University of California at Los Angeles School of Medicine, Los Angeles, California 90095
J. Am. Chem. Soc., 2007, 129 (37), pp 11438–11446
DOI: 10.1021/ja072511s
Publication Date (Web): August 18, 2007
Copyright © 2007 American Chemical Society
†

 Iowa State University.

,
‡

 University of California at Los Angeles School of Medicine.

,
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, mhong@iastate.edu

Abstract

Abstract Image

The insertion of charged amino acid residues into the hydrophobic part of lipid bilayers is energetically unfavorable yet found in many cationic membrane peptides and protein domains. To understand the mechanism of this translocation, we measured the 13C−31P distances for an Arg-rich β-hairpin antimicrobial peptide, PG-1, in the lipid membrane using solid-state NMR. Four residues, including two Arg's, scattered through the peptide were chosen for the distance measurements. Surprisingly, all residues show short distances to the lipid 31P:  4.0−6.5 Å in anionic POPE/POPG membranes and 6.5−8.0 Å in zwitterionic POPC membranes. The shortest distance of 4.0 Å, found for a guanidinium Cζ at the β-turn, suggests N−H···O−P hydrogen bond formation. Torsion angle measurements of the two Arg's quantitatively confirm that the peptide adopts a β-hairpin conformation in the lipid bilayer, and gel-phase 1H spin diffusion from water to the peptide indicates that PG-1 remains transmembrane in the gel phase of the membrane. For this transmembrane β-hairpin peptide to have short 13C−31P distances for multiple residues in the molecule, some phosphate groups must be embedded in the hydrophobic part of the membrane, with the local 31P plane parallel to the β-strand. This provides direct evidence for toroidal pores, where some lipid molecules change their orientation to merge the two monolayers. We propose that the driving force for this toroidal pore formation is guanidinium−phosphate complexation, where the cationic Arg residues drag the anionic phosphate groups along as they insert into the hydrophobic part of the membrane. This phosphate-mediated translocation of guanidinium ions may underlie the activity of other Arg-rich antimocrobial peptides and may be common among cationic membrane proteins.

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History

  • Published In Issue September 19, 2007
  • Received April 11, 2007

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