Abstract
GPR174 is an immune-restricted G-protein-coupled receptor (GPCR) constitutively activated by lysophosphatidylserine (LysoPS). Elevated LysoPS in the tumor microenvironment may sustain GPR174 activity, promoting immunosuppression and resistance to cancer immunotherapies. Here, we modeled GPR174 bound to an antagonist mPS (modified LysoPS) and performed extensive molecular dynamics (MD) simulations in a heterogeneous lipid bilayer, with parallel simulations of the LysoPS-bound receptor for comparison. mPS binding inactivated GPR174 and resulted in reduced conformational dynamics, persistent hydrogen bonding interactions, and selective interactions with transmembrane helix 1. In contrast, LysoPS exhibited greater conformational flexibility, multiple binding poses, and transient acyl chain displacement into the membrane. Network analysis revealed that LysoPS engaged conserved activation motifs (PIF, DRY, N/DPxxY) to couple the ligand binding site to the G-protein interface, whereas these pathways were disrupted by mPS. Protein-lipid analyses further suggested that membrane lipids, including phosphatidylinositol (PIP2), modulate ligand dynamics and receptor conformational states. Collectively, these findings highlight distinct ligand-specific mechanisms of GPR174 modulation and provide a framework for rational design of selective antagonists with immunotherapeutic potential.