Contributors: Génétique et Physiologie de l'Audition; Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut Pasteur Paris (IP)-Institut National de la Santé et de la Recherche Médicale (INSERM); Biophysique des Macromolécules et de leurs Interactions; Institut Pasteur Paris (IP)-Centre National de la Recherche Scientifique (CNRS); Institut Curie Paris; Institut Pasteur Paris (IP); Collège de France (CdF (institution)); This work was supported by LHW-Stiftung, Fondation Orange, Conny Maeva Foundation, ANR-05-MRAR-015-01, Raymonde and Guy Strittmatter Foundation (under the aegis of Fondation de France), FAUN Stiftung (Suchert Foundation). Funding to pay the Open Access Charge was provided by Unite de Genetique et Physiologie de l'Audition, Institut Pasteur, France.; The authors thank Muriel Delepierre for NMR spectra, Raphaël Etournay and Alexandre Chenal for their advice in the preparation of LUV, Beatrice Amigues for myosin VIIa tail preparation, Bruno Baron for circular dichroism experiments, Jacqueline Levilliers for her help in the manuscript preparation and the staff of Dynamic Imaging platform of the Pasteur Institute.; ANR-05-MRAR-0015,Usher type I,Physiopathologie du syndrome de Usher de type I : de la structure de la myosine VIIa et de l'harmonine à leur fonction dans les cellules ciliées auditives(2005)
نبذة مختصرة : International audience ; Cadherin-23 is a component of early transient lateral links of the auditory sensory cells' hair bundle, the mechanoreceptive structure to sound. This protein also makes up the upper part of the tip links that control gating of the mechanoelectrical transduction channels. We addressed the issue of the molecular complex that anchors these links to the hair bundle F-actin core. By using surface plasmon resonance assays, we show that the cytoplasmic regions of the two cadherin-23 isoforms that do or do not contain the exon68encoded peptide directly interact with harmonin, a submembrane PDZ (post-synaptic density, disc large, zonula occludens) domain-containing protein, with unusually high affinity. This interaction involves the harmonin Nter-PDZ1 supramodule, but not the C-terminal PDZ-binding motif of cadherin-23. We establish that cadherin-23 directly binds to the tail of myosin VIIa. Moreover, cadherin-23, harmonin and myosin VIIa can form a ternary complex, which suggests that myosin VIIa applies tension forces on hair bundle links. We also show that the cadherin-23 cytoplasmic region, harmonin and myosin VIIa interact with phospholipids on synthetic liposomes. Harmonin and the cytoplasmic region of cadherin-23, both independently and as a binary complex, can bind specifically to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2), which may account for the role of this phospholipid in the adaptation of mechanoelectrical transduction in the hair bundle. The distributions of cadherin-23, harmonin, myosin VIIa and PI(4,5)P 2 in the growing and mature auditory hair bundles as well as the abnormal locations of harmonin and myosin VIIa in cadherin-23 null mutant mice strongly support the functional relevance of these interactions.
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