TAM receptor-ligand interfaces in zebrafish and mammals: A comparative structural and electrostatic analysis

Efficient resolution of neuroinflammation and debris clearance are key determinants of successful central nervous system (CNS) regeneration. Regenerative vertebrates such as Danio rerio often show faster immune resolution and debris clearance than mammals, yet the molecular determinants underlying these differences remain incompletely understood. TAM receptor tyrosine kinases (Tyro3, Axl, and Mertk) and their ligands Gas6 and Protein S are central regulators of phagocytosis and immune resolution in the nervous system, but whether intrinsic structural properties of these receptor-ligand complexes may modulate TAM signaling across species with distinct regenerative capacities has not been systematically explored. Here, I perform a comparative in silico analysis of TAM receptors and ligands from zebrafish, human, and mouse, integrating sequence evolution, high-confidence structural modeling, interface characterization, and electrostatic analysis. Despite substantial sequence divergence between mammals and zebrafish, ligand-binding domains retain strong structural conservation, supporting a conserved global mode of TAM-ligand engagement. At the interface level, zebrafish complexes exhibit enhanced electrostatic contributions and increased salt-bridge density, particularly in the Tyro3-Protein S interaction. Residue-resolved electrostatic analysis identifies clustered interface hotspots that are conserved in spatial organization and physicochemical function across species, despite evolutionary rewiring of individual contacts. Together, these findings suggest that TAM receptor-ligand interfaces are evolutionarily tuned through subtle electrostatic and geometric variation rather than large-scale structural changes. This conserved yet adaptable electrostatic framework supports the hypothesis that interface-level features may modulate TAM receptor-ligand engagement across vertebrates. However, these structural and electrostatic properties should be interpreted as potential modulatory contributions to TAM signaling rather than definitive determinants of regenerative capacity.