Temperature dependence of binding entropy drives evolution in LacI family proteins.

Enthalpy-driven ligand binding emerges in the most recent ancestor and extant LacI, contrasting with entropy-driven binding in the most distant ancestor of the LacI/GalR family (LGF) transcription factors.

• Why it matters: Thermodynamic determinants of how ligand specificity evolves are unclear, especially how enthalpy–entropy trade-offs shift across evolutionary time and environmental conditions.
• What they did: The study compares binding thermodynamics across ancestral and extant LGF transcription factors, linking entropy-driven binding to open, dynamic conformations and proposing entropic reservoirs.
• The result: The thermodynamic shift is consistent with adaptation to cooling, implying binding mechanisms evolved to favor enthalpic modes when temperatures decrease.

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