{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T16:53:02Z","timestamp":1785430382894,"version":"3.56.0"},"posted":{"date-parts":[[2025,9,25]]},"group-title":"Biochemistry","reference-count":85,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2025,9,25]],"date-time":"2025-09-25T00:00:00Z","timestamp":1758758400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"DOI":"10.13039\/100015326","name":"NIH Common Fund","doi-asserted-by":"crossref","award":["DP5OD036136"],"award-info":[{"award-number":["DP5OD036136"]}],"id":[{"id":"10.13039\/100015326","id-type":"DOI","asserted-by":"crossref"}]},{"award":["Sandler Fellowship"],"award-info":[{"award-number":["Sandler Fellowship"]}],"id":[{"id":"https:\/\/ror.org\/043mz5j54","id-type":"ROR","asserted-by":"publisher"}]},{"award":["5R25GM056847-25"],"award-info":[{"award-number":["5R25GM056847-25"]}],"id":[{"id":"https:\/\/ror.org\/01cwqze88","id-type":"ROR","asserted-by":"publisher"}]},{"name":"Achievement Rewards for College Scientists"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,2,18]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                <jats:p>Norrin is an atypical ligand that regulates retinal angiogenesis through the Wnt\/\u03b2-catenin pathway. Norrin triggers heterodimerization of Frizzled-4 (FZD4) with Low-density lipoprotein receptor-related protein 5 or 6 (LRP5\/6), leading to downstream \u03b2-catenin stabilization. Unlike Wnt ligands, Norrin requires the tetraspanin Tspan12 for signaling amplification, but it is not understood why. Here, we report a 3.4-angstrom structure of Tspan12 in complex with FZD4 determined by cryo-electron microscopy. The structure reveals that FZD4 and Tspan12 form a direct complex in the absence of Norrin. The transmembrane (TM) domain of Tspan12 is oriented in a tightly packed four-helix bundle and interacts with TM2 of FZD4 to promote trafficking of Tspan12 to the cell surface. The C-D helices of Tspan12, which mediate binding to Norrin, remain exposed while Tspan12 is in complex with FZD4, facilitating higher-affinity Norrin binding. Cell-based assays reveal that Tspan12 and FZD4 remain associated after Norrin recognition, suggesting that Tspan12 is a core component of the FZD4-Norrin-LRP5\/6 signaling complex. Together, these studies reveal the molecular mechanism underlying the assembly of the Tspan12-FZD4 complex and the enhancement of Norrin signaling, suggesting new ways to target the FZD4-Tspan12 complex for ocular diseases characterized by hypo- or hyper-vascularization.<\/jats:p>\n                <jats:sec>\n                  <jats:title>SIGNIFICANCE STATEMENT<\/jats:title>\n                  <jats:p>Blood vessel formation in the retina is essential for vision, and its disruption leads to ocular diseases. Norrin regulates retinal angiogenesis by triggering the heterodimerization of Frizzled-4 with co-receptor LRP5\/6, mimicking the function of Wnt ligands and leading to downstream \u03b2-catenin signaling. Unlike Wnts, Norrin requires a tetraspanin family member, Tspan12, to amplify signaling. We report the structure of the FZD4-Tspan12 co-receptor complex and identify key interacting regions that enable Tspan12 trafficking to the cell surface and higher affinity capture of Norrin. Cell-based assays indicate Tspan12 remains a component of the active Norrin-FZD4-LRP5\/6 signaling complex. Our results highlight an underappreciated role of tetraspanins in direct regulation of receptor signaling and suggest new therapeutic avenues for targeting abnormalities in vascular growth.<\/jats:p>\n                <\/jats:sec>","DOI":"10.1101\/2025.09.25.678640","type":"posted-content","created":{"date-parts":[[2025,9,26]],"date-time":"2025-09-26T06:30:15Z","timestamp":1758868215000},"source":"Crossref","is-referenced-by-count":0,"title":["Structural basis for regulation of Frizzled-4 signaling by the co-receptor Tetraspanin-12"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0009-0006-1409-2382","authenticated-orcid":false,"given":"Alyana J.","family":"Granados","sequence":"first","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7170-6866","authenticated-orcid":false,"given":"Payal P.","family":"Pratap","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3829-357X","authenticated-orcid":false,"given":"Kevin Alexander Estrada","family":"Alamo","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA"},{"name":"Program in Biophysics, University of California, San Francisco, CA 94158, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0077-667X","authenticated-orcid":false,"given":"Katherine J.","family":"Susa","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026022112450393000_2025.09.25.678640v2.1","doi-asserted-by":"publisher","DOI":"10.1016\/j.devcel.2009.06.016"},{"key":"2026022112450393000_2025.09.25.678640v2.2","doi-asserted-by":"publisher","DOI":"10.1016\/j.tips.2007.09.001"},{"key":"2026022112450393000_2025.09.25.678640v2.3","doi-asserted-by":"publisher","DOI":"10.1038\/382225a0"},{"key":"2026022112450393000_2025.09.25.678640v2.4","doi-asserted-by":"publisher","DOI":"10.1038\/35083601"},{"key":"2026022112450393000_2025.09.25.678640v2.5","doi-asserted-by":"publisher","DOI":"10.1126\/science.1222879"},{"key":"2026022112450393000_2025.09.25.678640v2.6","doi-asserted-by":"publisher","DOI":"10.1038\/35035117"},{"key":"2026022112450393000_2025.09.25.678640v2.7","doi-asserted-by":"publisher","DOI":"10.1016\/S1097-2765(03)00427-1"},{"key":"2026022112450393000_2025.09.25.678640v2.8","doi-asserted-by":"publisher","DOI":"10.1126\/science.1137065"},{"key":"2026022112450393000_2025.09.25.678640v2.9","doi-asserted-by":"publisher","DOI":"10.1146\/annurev-biochem-040320-103615"},{"key":"2026022112450393000_2025.09.25.678640v2.10","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.cellbio.14.1.59"},{"key":"2026022112450393000_2025.09.25.678640v2.11","doi-asserted-by":"publisher","DOI":"10.1038\/ng0692-204"},{"key":"2026022112450393000_2025.09.25.678640v2.12","doi-asserted-by":"publisher","DOI":"10.1038\/ng0692-199"},{"key":"2026022112450393000_2025.09.25.678640v2.13","doi-asserted-by":"publisher","DOI":"10.1101\/gad.228544.113"},{"key":"2026022112450393000_2025.09.25.678640v2.14","doi-asserted-by":"publisher","DOI":"10.1038\/ng1092-139"},{"key":"2026022112450393000_2025.09.25.678640v2.15","doi-asserted-by":"publisher","DOI":"10.1038\/nrm3470"},{"key":"2026022112450393000_2025.09.25.678640v2.16","doi-asserted-by":"publisher","DOI":"10.1016\/S0092-8674(04)00216-8"},{"key":"2026022112450393000_2025.09.25.678640v2.17","doi-asserted-by":"publisher","DOI":"10.1016\/j.molmed.2010.07.003"},{"key":"2026022112450393000_2025.09.25.678640v2.18","doi-asserted-by":"publisher","DOI":"10.1002\/humu.21250"},{"key":"2026022112450393000_2025.09.25.678640v2.19","doi-asserted-by":"crossref","unstructured":"L.-Y. 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