The unexpected binding capacity of the third PDZ domain of whirlin to cochlear hair cell partners Hearing is a mechanical and neurochemical various cellular partners, most of them being unknown. In this process, which occurs in the hair cells of inner study, we characterized at the molecular level the interaction of the whirlin third PDZ domain with various cellular partners. ear that converts the sound vibrations into electrical signals transmitted to the brain. EXPERIMENTAL RESULTS The multi-PDZ scaffolding protein whirlin In the full-length whirlin, the third PDZ domain is localized at the plays a critical role in the formation and C-terminal end of the protein and linked to the HHD2 domain function of stereocilia exposed at the surface through a large PR region. We investigated the conformation of several constructs of the C-terminal domain using small of hair cells. We identified seven stereociliary angle X-ray scattering (SAXS) (Fig. 1). Overall, our SAXS results proteins that encode PDZ binding motifs and demonstrated that the PDZ3 domain is independent from the interact with the third PDZ domain of whirlin other folded domain HHD2, in the larger molecular context of whirlin; it is linked to the rest of the molecule by flexible sequence and solved the atomic resolution structures as illustrated by the large radius of gyration and maximum of four complexes. Our results extend our distances and by the plateau at large q-values observed in the understanding of the binding plasticity of dimensionless Kratky plot. It is therefore useful to study this domain as an independent feature of the whirlin. whirlin and further confirm its multiple roles in the development of sensory cells and its FIGURE 1 relation with non-syndromic deafness. The sense of hearing is a mechanical, chemical and electrical process, that requires highly specialized sensory cells (hair cells) in the cochlea of the inner ear [1]. At their apical surfaces, three rows of staircase-like actin-filled stereocilia are connected by different types of extracellular links. During hair cell development, the hair bundle harbours transient links called ankle links located at the stereocilia base. Ankle links are anchored to large protein complex in the submembrane region. Most of the proteins that form these anchoring densities are called Usher proteins, as mutations altering their function cause the Usher syndrome (USH), that is the most common form of hereditary hearing-vision loss in humans [2]. Usher proteins are also found in retina photoreceptor cells. Usherin and ADGRV1 are two large transmembrane Usher proteins make part of the ankle link complex and are associated to the PDZ-scaffold proteins whirlin and PDZD7 in the cytoplasm [3]. Whirlin is a multi-domain scaffolding protein, which is essential for the bundling and elongation of stereocilia of the hair cells [4]. Human whirlin is composed of 907 amino acids and encompasses two Harmonin Homology Domains (HHD), three PDZ domains, a proline-rich (PR) region and a C-terminal PBM (PDZ binding motif) (Fig.1). Whirlin is expected to participate in dynamical and transient complexes in rather different cellular environments, and consequently to interact with 54