Entropy in the Molecular Recognition of Membrane Protein-Lipid Interactions

Understanding the molecular driving forces that underlie membrane protein-lipid interactions requires the characterization of their binding thermodynamics. Here, we employ variable-temperature native mass spectrometry to determine the thermodynamics of lipid binding events to the human G-protein-gated inward rectifier potassium channel, Kir3.2. The channel displays distinct thermodynamic strategies to engage phosphatidylinositol (PI) and phosphorylated forms thereof. The addition of a 4'-phosphate to PI results in an increase in favorable entropy. PI with two or more phosphates exhibits more complex binding, where lipids appear to bind two nonidentical sites on Kir3.2. Remarkably, the interaction of 4,5-bisphosphate PI with Kir3.2 is solely driven by a large, favorable change in entropy. Installment of a 3'-phosphate to PI(4,5)P-2 results in an altered thermodynamic strategy. The acyl chain of the lipid has a marked impact on binding thermodynamics and, in some cases, enthalpy becomes favorable.

Automated summary

This study used variable-temperature native mass spectrometry to investigate the thermodynamics of lipid binding events to the human G-protein-gated inward rectifier potassium channel, Kir3.2, revealing distinct thermodynamic strategies for different types of phosphatidylinositol and phosphorylated forms. The acyl chain of the lipid and the number of phosphate groups have significant impacts on the binding thermodynamics, with entropy and enthalpy playing key roles in the interactions.