Host membrane cholesterol constrains constitutive signaling of the oncogenic KSHV GPCR ORF74
Cholesterol is a major structural component of the plasma membrane and a key allosteric regulator of G protein-coupled receptors (GPCRs), yet its role in controlling constitutive receptor activity remains poorly understood. Virally encoded GPCRs provide an ideal system to address this question because many exhibit constitutive signaling that promotes viral persistence and pathogenesis, although…
Cholesterol, a major structural element of cellular membranes, also functions as an allosteric regulator for G protein-coupled receptors (GPCRs). However, the specific mechanisms by which viruses, which rely on these receptors for their persistence and pathogenicity, utilize host cholesterol to control constitutive receptor activity are not fully understood.
In this study, researchers identified a novel cholesterol-dependent allosteric mechanism employed by the oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV) GPCR ORF74 to regulate its constitutive signaling. Using cryo-electron microscopy (cryoEM) structural analysis, the team discovered a cholesterol-binding pocket formed by transmembrane helices 3, 5, and 6 that is exclusively present in the inactive receptor state.
This cholesterol-binding site is crucial for restraining the outward movement of transmembrane helix 6, stabilizing the inactive conformation of the receptor, and suppressing spontaneous receptor activation. Molecular dynamics simulations further supported these findings, demonstrating that cholesterol binding directly influences receptor conformation and activity.
Notably, the study revealed that altering the canonical DRY motif to a non-canonical VRY motif exposes a conserved residue (R1433.50), creating a new membrane-facing cholesterol-binding interface. This modification effectively links membrane cholesterol levels to receptor conformational control. To investigate the implications of this regulatory mechanism, the researchers conducted experiments where cellular cholesterol levels were manipulated.
They found that lowering cellular cholesterol levels enhanced ORF74 signaling, while disrupting the cholesterol-binding interaction impaired receptor stabilization. These observations suggest that KSHV has evolved a sophisticated strategy to exploit host lipid-dependent allosteric regulation to optimize its constitutive signaling, highlighting the virus's ability to adapt to and manipulate the cellular environment for its benefit.
Written by urgent.news from bioRxiv's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
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