title: Photodamage of lipid bilayers by irradiation of a fluorescently labeled cell-penetrating peptide.
abstract: BACKGROUND
  Fluorescently labeled cell-penetrating peptides can translocate into cells by endocytosis and upon light irradiation, lyse the endocytic vesicles. This photo-inducible endosomolytic activity of Fl-CPPs can be used to efficiently deliver macromolecules such as proteins and nucleic acids and other small organic molecules into the cytosol of live cells. The requirement of a light trigger to induce photolysis provides a more spatial and temporal control to the intracellular delivery process.
  
  
  METHODS
  In this report, we examine the molecular level mechanisms by which cell-penetrating peptides such as TAT when labeled with small organic fluorophore molecules acquire a photo-induced lytic activity using a simplified model of lipid vesicles.
  
  
  RESULTS
  The peptide TAT labeled with 5(6)-carboxytetramethylrhodamine binds to negatively charged phospholipids, thereby bringing the fluorophore in close proximity to the membrane of liposomes. Upon light irradiation, the excited fluorophore produces reactive oxygen species at the lipid bilayer and oxidation of the membrane is achieved. In addition, the fluorescent peptide causes aggregation of photo-oxidized lipids, an activity that requires the presence of arginine residues in the peptide sequence.
  
  
  CONCLUSIONS
  These results suggest that the cell-penetrating peptide plays a dual role. On one hand, TAT targets a conjugated fluorophore to membranes. On the other hand, TAT participates directly in the destabilization of photosensitized membranes. Peptide and fluorophore therefore appear to act in synergy to destroy membranes efficiently.
  
  
  CONCLUSIONS
  Understanding the mechanism behind Fl-CPP mediated membrane photodamage will help to design optimally photo-endosomolytic compounds.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, United States.
authors.forename: Igor
authors.initials: I
authors.lastname: Meerovich
authors.forename: Nandhini
authors.initials: N
authors.lastname: Muthukrishnan
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Johnson
authors.forename: Alfredo
authors.initials: A
authors.lastname: Erazo-Oliveras
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Pellois
mesh_terms: D002462:Cell Membrane / Q000187:drug effects* / Q000528:radiation effects; D002463:Cell Membrane Permeability / Q000187:drug effects* / Q000528:radiation effects; D057846:Cell-Penetrating Peptides / Q000737:chemistry / Q000494:pharmacology*; D004705:Endocytosis; D005456:Fluorescent Dyes; D006801:Humans; D008027:Light / Q000009:adverse effects*; D008051:Lipid Bilayers / Q000737:chemistry* / Q000528:radiation effects; D008081:Liposomes; D010782:Photolysis; D017319:Photosensitizing Agents / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012235:Rhodamines / Q000737:chemistry / Q000378:metabolism; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000737:chemistry / Q000494:pharmacology*
chemical_list: C437523:5-carboxytetramethylrhodamine; D057846:Cell-Penetrating Peptides; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species; D012235:Rhodamines; D054322:tat Gene Products, Human Immunodeficiency Virus
keywords: BMP; CPP; Cell-penetrating peptide; Fl–CPP; LUV; Liposome; N,N,N′,N′-tetramethyl-1,4-phenylenediamine; NBT; PBS; PC; PCI; PS; Photochemical internalization; Photolysis; PnA; RB; RNO; ROS; TAT; TMPD; TMR; bis(monoacylglycero)-phosphate; cell-penetrating peptide; cis-parinaric (9Z,11E,13E,15Z-octadecatetraenoic) acid; fluorophore/cell-penetrating peptide conjugate; large unilamellar vesicle; nitro blue tetrazolium; p-nitrosodimethylaniline; phosphate buffered saline; phosphatidylcholine; phosphatidylserine; photochemical internalization; protein transduction domain of Human Immunodeficiency Virus 1 trans-activating transcriptional activator; reactive oxygen species; rose bengal; tetramethylrhodamine