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However, the sequence of structural events from G protein recognition to GDP release has remained elusive. Here, we leveraged the viral chemokine GPCR US28 to capture multiple activation states of the US28-G\n                  <jats:sub>q<\/jats:sub>\n                  complex. Using cryo-electron microscopy and an engineered chemokine superagonist, we determined three distinct complex structures, capturing a GDP-bound Encounter state, the nucleotide-free Canonical state, and a putative intermediate bridging the two states, the Transition-to-Canonical state. These structures, along with simulations and functional data, provide high-resolution snapshots of a plausible G protein activation trajectory and support a stepwise conformational model for G protein activation. This activation cascade closely parallels mechanisms proposed for human GPCRs, suggesting a conserved GPCR signaling mechanism.\n                <\/jats:p>","DOI":"10.64898\/2025.12.10.692789","type":"posted-content","created":{"date-parts":[[2025,12,11]],"date-time":"2025-12-11T03:55:16Z","timestamp":1765425316000},"source":"Crossref","is-referenced-by-count":0,"title":["Structural basis of stepwise G protein activation by the viral chemokine receptor US28"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3675-5136","authenticated-orcid":false,"given":"Kevin M.","family":"Jude","sequence":"first","affiliation":[{"name":"Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA, USA"},{"name":"Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA"},{"name":"Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2445-8791","authenticated-orcid":false,"given":"Carl-Mikael","family":"Suomivuori","sequence":"additional","affiliation":[{"name":"Department of Pharmacology, Yale School of Medicine, New Haven, CT, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Deepa","family":"Waghray","sequence":"additional","affiliation":[{"name":"Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7762-9793","authenticated-orcid":false,"given":"Shoji","family":"Maeda","sequence":"additional","affiliation":[{"name":"Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8070-1493","authenticated-orcid":false,"given":"Yoshinori","family":"Fujiyoshi","sequence":"additional","affiliation":[{"name":"Cellular and Structural Physiology Laboratory, Institute of Integrated Research, Institute of Science Tokyo, Bunkyo, Tokyo, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0805-4049","authenticated-orcid":false,"given":"Asuka","family":"Inoue","sequence":"additional","affiliation":[{"name":"Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan"},{"name":"Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9273-0278","authenticated-orcid":false,"given":"K. 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