Structural basis for ligand promiscuity and high signaling activity of Kaposi’s Sarcoma-associated Herpesvirus-encoded GPCR
- Jun Bae Park
- Bibekananda Sahoo
- Amita Rani Sahoo
- Dokyun Kim
- Hogyu David Seo
- James Bowman
- Mi-Jeong Kwak
- Sophia Suh
- Matthias Buck
- Xinghong Dai
- Jae U. Jung
2025-09-25
Kaposi’s Sarcoma-associated Herpesvirus encodes ORF74, a viral G protein-coupled receptor homologous to CXCR2, which plays a crucial role in Kaposi’s Sarcoma development through its high basal signaling activity. Our cryoEM analysis of ORF74 in ligand-free, BRIL-fused ligand-free, and CXCL1/Gi trimer -bound forms elucidates its ligand-independent signaling activity. A widely open, static extracellular cavity facilitates ligand promiscuity by enabling dynamic access and diverse binding modes. Structural alterations in CWxP, E/DRY, and NPxxY micro-switches stabilize the active conformation, leading to constitutive signaling. Metadynamics simulations reveal a dynamic ensemble between local switch structures corresponding to the inactive and active states, supporting spontaneous activation. CXCR2-ORF74 chimeras highlight intracellular loops 2 and 3 as key modulators of basal and agonist-induced activity. This study defines the structural basis of ORF74’s ligand promiscuity, spontaneous activation, and high basal signaling, providing insights into its role in viral oncogenesis.