Capturing Dynamic Transporter-Lipid Interactions

Abstract

Membrane proteins are dynamic biomolecules responsible for many critical cellular functions. Transporters, a subclass of membrane proteins, play crucial roles for maintaining adequate conditions for life by moving diverse biomolecules across the biological membrane. Lipids surrounding transporters play key roles in ensuring correct protein function. Accumulating evidences suggest that transporters function as complexes with their surrounding membrane lipids. Despite advances on understanding membrane protein-lipid interactions, our knowledge of the role of lipids in mediating protein dynamics remains limited. Here, we showcase how membrane lipids impact on the oligomeric state and conformational dynamics of transporters. We show using native mass spectrometry on a eukaryotic purine symporter that specific lipids binding to the protein modulate the formation of its oligomeric states. Mechanistically, such lipid modulation is obtained through specific interactions of structural lipids with the protein, which has a stabilising effect in the protein interface. We also show using the emerging and powerful method of hydrogen-deuterium exchange mass spectrometry (HDX-MS) that specific lipid-protein interactions modulate the conformational dynamics of the homologous transporters LacY and XylE from the major facilitator superfamily (MFS), the largest family of transporters. Specifically, we reveal that phosphatidylethanolamine (PE) lipids interfere with the formation of their conserved networks, critical for stabilising transporter states, thus unravelling a generic mechanism for the conformational transitions of MFS transporters between different states. Overall, this work allows us to establish that the dynamics of transporter-lipid assemblies can be captured in solution, enabling us to define changes in the conformation of membrane proteins at high resolution.