title: Examining the proteins of functional retinal lipofuscin using proteomic analysis as a guide for understanding its origin.
abstract: OBJECTIVE
  To elucidate the origins of biologically active retinal lipofuscin (RLF) by examining its protein composition.
  
  
  METHODS
  Total protein and total lipid were extracted and quantified. Proteins in this lipoprotein granule were identified by limited-scale proteomic analysis using both two-dimensional (2D) gel electrophoresis and SDS-PAGE coupled with MALDI-QqToF MSMS and automated LCMSMS, respectively.
  
  
  RESULTS
  RLF granules were 44% protein and 50% lipid. Proteomic analyses identified 41 constituent proteins. Hydrophobic proteins and several proteins specific to photoreceptors, including rhodopsin, that have not previously been reported, were identified. Extensive protein modification, especially oxidative damage, was observed.
  
  
  CONCLUSIONS
  Proteins identified support the model that RLF accumulates in RPE cells as a result of the buildup of undigested material from the phagocytosis of photoreceptor outer segments. Perhaps oxidative damage renders some of these proteins indigestible and thus leads to the accumulation of RLF granules.
authors.affiliation: Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Warburton
authors.forename: Katie
authors.initials: K
authors.lastname: Southwick
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Hardman
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Secrest
authors.forename: Ryan K
authors.initials: RK
authors.lastname: Grow
authors.forename: Huijun
authors.initials: H
authors.lastname: Xin
authors.forename: Adam T
authors.initials: AT
authors.lastname: Woolley
authors.forename: Gregory F
authors.initials: GF
authors.lastname: Burton
authors.forename: Craig D
authors.initials: CD
authors.lastname: Thulin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D006801:Humans; D008062:Lipofuscin / Q000032:analysis*; D008855:Microscopy, Electron, Scanning; D016253:Microscopy, Immunoelectron; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000737:chemistry* / Q000648:ultrastructure; D020543:Proteome / Q000032:analysis*; D040901:Proteomics; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D008062:Lipofuscin; D020543:Proteome