title: Structure, topology, and tilt of cell-signaling peptides containing nuclear localization sequences in membrane bilayers determined by solid-state NMR and molecular dynamics simulation studies.
abstract: Cell-signaling peptides have been extensively used to transport functional molecules across the plasma membrane into living cells. These peptides consist of a hydrophobic sequence and a cationic nuclear localization sequence (NLS). It has been assumed that the hydrophobic region penetrates the hydrophobic lipid bilayer and delivers the NLS inside the cell. To better understand the transport mechanism of these peptides, in this study, we investigated the structure, orientation, tilt of the peptide relative to the bilayer normal, and the membrane interaction of two cell-signaling peptides, SA and SKP. Results from CD and solid-state NMR experiments combined with molecular dynamics simulations suggest that the hydrophobic region is helical and has a transmembrane orientation with the helical axis tilted away from the bilayer normal. The influence of the hydrophobic mismatch, between the hydrophobic length of the peptide and the hydrophobic thickness of the bilayer, on the tilt angle of the peptides was investigated using thicker POPC and thinner DMPC bilayers. NMR experiments showed that the hydrophobic domain of each peptide has a tilt angle of 15 +/- 3 degrees in POPC, whereas in DMPC, 25 +/- 3 degree and 30 +/- 3 degree tilts were observed for SA and SKP peptides, respectively. These results are in good agreement with molecular dynamics simulations, which predict a tilt angle of 13.3 degrees (SA in POPC), 16.4 degrees (SKP in POPC), 22.3 degrees (SA in DMPC), and 31.7 degrees (SKP in DMPC). These results and simulations on the hydrophobic fragment of SA or SKP suggest that the tilt of helices increases with a decrease in bilayer thickness without changing the phase, order, and structure of the lipid bilayers.
authors.affiliation: Biophysics Research Division, University of Michigan, Ann Arbor, Michigan 48109-1055, USA. ramamoor@umich.edu
authors.forename: Ayyalusamy
authors.initials: A
authors.lastname: Ramamoorthy
authors.forename: Senthil K
authors.initials: SK
authors.lastname: Kandasamy
authors.forename: Dong-Kuk
authors.initials: DK
authors.lastname: Lee
authors.forename: Srikanth
authors.initials: S
authors.lastname: Kidambi
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Larson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D057927:Hydrophobic and Hydrophilic Interactions; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics; D008051:Lipid Bilayers / Q000737:chemistry; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000235:genetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D019913:Nuclear Localization Signals