title: Physicochemical mechanism for the enhanced ability of lipid membrane penetration of polyarginine.
abstract: Arginine-rich, cell-penetrating peptides (e.g., Tat-peptide, penetratin, and polyarginine) are used to carry therapeutic molecules such as oligonucleotides, DNA, peptides, and proteins across cell membranes. Two types of processes are being considered to cross the cell membranes: one is an endocytic pathway, and another is an energy-independent, nonendocytic pathway. However, the latter is still not known in detail. Here, we studied the effects of the chain length of polyarginine on its interaction with an anionic phospholipid large unilamellar vesicle (LUV) or a giant vesicle using poly-l-arginine composed of 69 (PLA69), 293 (PLA293), or 554 (PLA554) arginine residues, together with octaarginine (R8). ζ-potential measurements confirmed that polyarginine binds to LUV via electrostatic interactions. Circular dichroism analysis demonstrated that the transition from the random coil to the α-helix structure upon binding to LUV occurred for PLA293 and PLA554, whereas no structural change was observed for PLA69 and R8. Fluorescence studies using membrane probes revealed that the binding of polyarginine to LUV affects the hydration and packing of the membrane interface region, in which the degree of membrane insertion is greater for the longer polyarginine. Isothermal titration calorimetry measurements demonstrated that although the binding affinity (i.e., the Gibbs free energy of binding) per arginine residue is similar among all polyarginines the contribution of enthalpy to the energetics of binding of polyarginine increases with increasing polymer chain length. In addition, confocal laser scanning microscopy showed that all polyarginines penetrate across giant vesicle membranes, and the order of the amount of membrane penetration is R8 ≈ PLA69 < PLA293 ≈ PLA554. These results suggest that the formation of α-helical structure upon lipid binding drives the insertion of polyarginine into the membrane interior, which appears to enhance the membrane penetration of polyarginine.
authors.affiliation: Institute of Health Biosciences and Graduate School of Pharmaceutical Sciences, The University of Tokushima, Tokushima 770-8505, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takechi
authors.forename: Haruka
authors.initials: H
authors.lastname: Yoshii
authors.forename: Masafumi
authors.initials: M
authors.lastname: Tanaka
authors.forename: Toru
authors.initials: T
authors.lastname: Kawakami
authors.forename: Saburo
authors.initials: S
authors.lastname: Aimoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Saito
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D055598:Chemical Phenomena; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D010539:Permeability; D017433:Protein Structure, Secondary; D021381:Protein Transport; D053835:Unilamellar Liposomes / Q000737:chemistry / Q000378:metabolism
chemical_list: D010455:Peptides; D053835:Unilamellar Liposomes; C015462:polyarginine