Characterization of the ternary Usher syndrome SANS/ush2a/whirlin protein complex

Hum Mol Genet. 2017 Mar 15;26(6):1157-1172. doi: 10.1093/hmg/ddx027.

Abstract

The Usher syndrome (USH) is the most common form of inherited deaf-blindness, accompanied by vestibular dysfunction. Due to the heterogeneous manifestation of the clinical symptoms, three USH types (USH1-3) and additional atypical forms are distinguished. USH1 and USH2 proteins have been shown to function together in multiprotein networks in photoreceptor cells and hair cells. Mutations in USH proteins are considered to disrupt distinct USH protein networks and finally lead to the development of USH.To get novel insights into the molecular pathomechanisms underlying USH, we further characterize the periciliary USH protein network in photoreceptor cells. We show the direct interaction between the scaffold protein SANS (USH1G) and the transmembrane adhesion protein ush2a and that both assemble into a ternary USH1/USH2 complex together with the PDZ-domain protein whirlin (USH2D) via mutual interactions. Immunohistochemistry and proximity ligation assays demonstrate co-localization of complex partners and complex formation, respectively, in the periciliary region, the inner segment and at the synapses of rodent and human photoreceptor cells. Protein-protein interaction assays and co-expression of complex partners reveal that pathogenic mutations in USH1G severely affect formation of the SANS/ush2a/whirlin complex. Translational read-through drug treatment, targeting the c.728C > A (p.S243X) nonsense mutation, restored SANS scaffold function. We conclude that USH1 and USH2 proteins function together in higher order protein complexes. The maintenance of USH1/USH2 protein complexes depends on multiple USH1/USH2 protein interactions, which are disrupted by pathogenic mutations in USH1G protein SANS.

MeSH terms

  • Deaf-Blind Disorders / genetics*
  • Deaf-Blind Disorders / pathology
  • Extracellular Matrix Proteins / chemistry
  • Extracellular Matrix Proteins / genetics*
  • Extracellular Matrix Proteins / metabolism
  • Hair Cells, Auditory / metabolism
  • Hair Cells, Auditory / pathology
  • Humans
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics*
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Mutation
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism
  • Photoreceptor Cells / metabolism
  • Photoreceptor Cells / pathology
  • Protein Binding
  • Protein Interaction Maps / genetics
  • Protein Structure, Tertiary
  • Usher Syndromes / complications
  • Usher Syndromes / genetics*
  • Usher Syndromes / pathology

Substances

  • Extracellular Matrix Proteins
  • Membrane Proteins
  • Multiprotein Complexes
  • Nerve Tissue Proteins
  • USH1G protein, human
  • USH2A protein, human
  • WHRN protein, human