*Review* **Assessing the Role of Lipids in the Molecular Mechanism of Membrane Proteins**

**Léni Jodaitis †, Thomas van Oene † and Chloé Martens \***

> Center for Structural Biology and Bioinformatics, Université Libre de Bruxelles, 1050 Brussels, Belgium; leni.jodaitis@ulb.be (L.J.); thomas.van.oene@ulb.be (T.v.O.)

**\*** Correspondence: chloe.martens@ulb.be

† These authors contributed equally.

**Abstract:** Membrane proteins have evolved to work optimally within the complex environment of the biological membrane. Consequently, interactions with surrounding lipids are part of their molecular mechanism. Yet, the identification of lipid–protein interactions and the assessment of their molecular role is an experimental challenge. Recently, biophysical approaches have emerged that are compatible with the study of membrane proteins in an environment closer to the biological membrane. These novel approaches revealed specific mechanisms of regulation of membrane protein function. Lipids have been shown to play a role in oligomerization, conformational transitions or allosteric coupling. In this review, we summarize the recent biophysical approaches, or combination thereof, that allow to decipher the role of lipid–protein interactions in the mechanism of membrane proteins.

**Keywords:** membrane protein; lipid–protein interaction; cryo-electron microscopy; hydrogen– deuterium exchange mass spectrometry; native mass spectrometry; single-molecule Förster resonance energy transfer; double electron–electron resonance; native mass spectrometry
