Structure of the conserved cytoplasmic C-terminal domain of occludin: identification of the ZO-1 binding surface

J Mol Biol. 2005 Sep 9;352(1):151-64. doi: 10.1016/j.jmb.2005.07.017.


Occludin is a transmembrane protein localized at tight junctions whose functions are complex yet poorly understood. Current evidence supports a role for occludin in both the formation of the paracellular barrier and in cell signaling. While the N-terminal extracellular domains of occludin mediate homotypic adhesion, the distal C-terminal cytoplasmic domain of occludin controls protein targeting and endocytosis. The C terminus can also bind to the scaffolding proteins ZO-1, ZO-2, ZO-3, cingulin, the membrane trafficking protein VAP33, and the cytoskeletal protein F-actin, suggesting an important role for this domain. This domain is highly homologous to an important functional domain in the C terminus of the ELL family of RNA polymerase II transcription factors. To explore the function of occludin, we determined the high-resolution crystal structure of its C-terminal distal cytoplasmic domain. The structure comprises three helices that form two separate anti-parallel coiled-coils and a loop that packs tightly against one of the coiled-coils. Using in vitro binding studies and site-directed mutagenesis, we have identified a large positively charged surface that contains the binding site for ZO-1, and this surface is required for proper localization of occludin to cell-cell junctions. On the basis of sequence conservation, we predict that occludin domains from different species and the C-terminal domain of the ELL transcription factors share a very similar structure. Our results provide a model to further test the function of occludin and its binding to other proteins.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Cell Line
  • Crystallography, X-Ray
  • Humans
  • Membrane Proteins / chemistry*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Occludin
  • Phosphoproteins / metabolism*
  • Protein Binding
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Sequence Alignment
  • Zonula Occludens-1 Protein


  • Membrane Proteins
  • OCLN protein, human
  • Occludin
  • Phosphoproteins
  • Recombinant Fusion Proteins
  • TJP1 protein, human
  • Zonula Occludens-1 Protein

Associated data

  • PDB/1WPA
  • PDB/1XAW