title: Whirlin and PDZ domain-containing 7 (PDZD7) proteins are both required to form the quaternary protein complex associated with Usher syndrome type 2.
abstract: Usher syndrome (USH) is the leading genetic cause of combined hearing and vision loss. Among the three USH clinical types, type 2 (USH2) occurs most commonly. USH2A, GPR98, and WHRN are three known causative genes of USH2, whereas PDZD7 is a modifier gene found in USH2 patients. The proteins encoded by these four USH genes have been proposed to form a multiprotein complex, the USH2 complex, due to interactions found among some of these proteins in vitro, their colocalization in vivo, and mutual dependence of some of these proteins for their normal in vivo localizations. However, evidence showing the formation of the USH2 complex is missing, and details on how this complex is formed remain elusive. Here, we systematically investigated interactions among the intracellular regions of the four USH proteins using colocalization, yeast two-hybrid, and pull-down assays. We show that multiple domains of the four USH proteins interact among one another. Importantly, both WHRN and PDZD7 are required for the complex formation with USH2A and GPR98. In this USH2 quaternary complex, WHRN prefers to bind to USH2A, whereas PDZD7 prefers to bind to GPR98. Interaction between WHRN and PDZD7 is the bridge between USH2A and GPR98. Additionally, the USH2 quaternary complex has a variable stoichiometry. These findings suggest that a non-obligate, short term, and dynamic USH2 quaternary protein complex may exist in vivo. Our work provides valuable insight into the physiological role of the USH2 complex in vivo and informs possible reconstruction of the USH2 complex for future therapy.
authors.affiliation: From the Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center.
authors.forename: Qian
authors.initials: Q
authors.lastname: Chen
authors.affiliation: From the Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center.
authors.forename: Junhuang
authors.initials: J
authors.lastname: Zou
authors.affiliation: From the Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center.
authors.forename: Zuolian
authors.initials: Z
authors.lastname: Shen
authors.affiliation: From the Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center.
authors.forename: Weiping
authors.initials: W
authors.lastname: Zhang
authors.affiliation: From the Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, the Department of Neurobiology and Anatomy, and the Department of Otolaryngology Head and Neck Surgery, University of Utah, Salt Lake City, Utah 84132 jun.yang@hsc.utah.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002522:Chlorocebus aethiops; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D054731:PDZ Domains; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D052245:Usher Syndromes / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D016326:Extracellular Matrix Proteins; D008565:Membrane Proteins; D043562:Receptors, G-Protein-Coupled; C485949:Adgrv1 protein, mouse; C000594656:PDZD7 protein, mouse; C491810:Ush2a protein, mouse; C477218:Whrn protein, mouse
keywords: GPR98; Hair Cell; PDZ Domain; PDZD7; Photoreceptor; Protein Complex; Protein-Protein Interaction; USH2A; Usher Syndrome; WHRN