Pathway-Dependent Energetics of SLC15A4–TASL Engagement: Single-Protomer Switching and Dimer-Interface Remodeling

Along the prescribed insertion pathway, TASL exhibited a pronounced apparent free-energy rise near the pocket, accompanied by rapid contact formation and a single-protomer switch from luminal-open to cytosolic-open, yielding a modeled asymmetric intermediate with altered cross-protomer interface geometry. TASL was stabilized by directional anchoring at a few key cationic sites. Pathway-dependent free-energy profiles further indicated that TASL engagement relaxed luminal-side interfacial stabilization and lowered the free-energy cost of inter-subunit separation without compromising pocket binding, potentially contributing to the formation of a signaling-competent SLC15A4–TASL module.

Finally, our results suggest that an inhibitor limits access to the TASL-permissive state by locking the luminal-open conformation and occupying the central cavity, increasing the free-energy cost along the prescribed TASL entry and reshaping electrostatic determinants. Together, these results connect experimentally resolved structural states through a computational energetic framework in which TASL-associated single-protomer switching may couple to luminal interface weakening and reduced interface persistence, motivating therapeutic strategies targeting the SLC15A4–TASL–IRF5 axis via conformational locking and competitive cavity occupation.