Cellular retinaldehyde-binding protein interacts with ERM-binding phosphoprotein 50 in retinal pigment epithelium

Invest Ophthalmol Vis Sci. 2004 Feb;45(2):393-401. doi: 10.1167/iovs.03-0989.


Purpose: To characterize mechanisms of apical localization of visual cycle components in retinal pigment epithelium (RPE) by the identification of cellular retinaldehyde-binding protein (CRALBP) interaction partners.

Methods: An overlay assay was used to detect interactions of CRALBP with components of RPE microsomes. Interacting proteins were identified with two-dimensional (2D)-PAGE and liquid chromatography tandem mass spectrometry (LC MS/MS). Protein interactions were characterized by affinity chromatography, peptide competition, and expression of protein domains. Protein colocalization in mouse retina was examined using double-label immunocytochemistry and confocal microscopy.

Results: CRALBP bound to a 54-kDa protein in RPE microsomes, which was identified as ERM (ezrin, radixin, moesin)-binding phosphoprotein 50 (EBP50), a PDZ domain protein, also known as sodium/hydrogen exchanger regulatory factory type 1 (NHERF-1). EBP50 and ezrin in solubilized microsomes bound to CRALBP-agarose but not to a control agarose column. CRALBP bound to both recombinant PDZ domains of EBP50 but not to the C-terminal ezrin-binding domain. In outer retina, EBP50 and ezrin were localized to RPE and Müller apical processes. CRALBP was distributed throughout both RPE and Müller cells, including their apical processes.

Conclusion: RM proteins are multivalent linkers that connect plasma membrane proteins with the cortical actin cytoskeleton. EBP50 interacts with ERM family members through a C-terminal domain and binds targets such as CRALBP through its PDZ domains, thus contributing to an apical localization of target proteins. Our results provide a structural basis for apical localization of a retinoid-processing complex in RPE cells and offer insight into the cell biology of retinoid processing and trafficking in RPE.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carrier Proteins / metabolism*
  • Cattle
  • Chromatography, Affinity
  • Chromatography, Liquid
  • Electrophoresis, Gel, Two-Dimensional
  • Humans
  • Mass Spectrometry
  • Mice
  • Microscopy, Confocal
  • Microsomes / metabolism
  • Phosphoproteins / metabolism*
  • Pigment Epithelium of Eye / metabolism*
  • Protein Binding
  • Protein Interaction Mapping
  • Retinaldehyde / metabolism*
  • Sodium-Hydrogen Exchangers*


  • 11-cis-retinal-binding protein
  • Carrier Proteins
  • Phosphoproteins
  • Sodium-Hydrogen Exchangers
  • sodium-hydrogen exchanger regulatory factor
  • Retinaldehyde