Speaker
Description
Cellular membranes are highly complex composite materials composed of lipids and proteins. The diverse physiological functions of these membranes, such as transport of molecules or signaling are controlled by intricate interactions between lipids and proteins across molecular to mesoscopic length scales. Among these, interactions due to a mismatch between the hydrophobic length of integral membrane proteins and the hydrophobic thickness of their hosting lipid bilayers may modulate protein conformational equilibrium and thereby influence their function.
In this project, we used the well-examined outer membrane phospholipase A (OmpLA) to observe the impact of hydrophobic mismatch on protein-protein interactions at the single molecule level. OmpLA hydrolyses phospholipids upon the formation of homodimers. We thus reconstituted a fluorescently labeled and inactive variant of OmpLA into lipid vesicles to probe its dimerization equilibrium as proxy for its activity. Specifically, we used single molecule Förster resonance energy transfer (smFRET) on a custom-built single molecule confocal microscope, which allowed to simultaneously keep track of the interprotein distance and the stoichiometry of FRET pairs. Control experiments of OmpLA dimerization were performed in zwitterionic micelles. By systematically varying lipid composition, we explored conditions of positive and negative hydrophobic mismatch and identified distinct effects on OmpLA dimerization behaviour. Our results demonstrate how bulk membrane properties can regulate the interactions and functional states of integral membrane proteins, providing insights into the physical mechanisms underlying the coupling of bulk membrane properties and integral membrane proteins.