Effects of non-ionic and zwitterionic detergents on soluble proteins during native mass spectrometry experiments

Detergents are commonly employed for solubilization and stabilization of integral membrane proteins. Their effects on the charge states of detergent-solubilized membrane proteins in native mass spectrometry measurements have previously been described. These effects can be mediated through the transmembrane region directly interacting with the detergent micelle or through the soluble domains of the proteins getting in close contact with detergent micelles during electrospray ionization. Here, we explore the effects of detergent micelles on soluble proteins during native mass spectrometry aiming at distinguishing these two events. Specifically, we employ two non-ionic and one zwitterionic detergents as well as a variety of standard proteins differing in size, oligomeric state and surface hydrophobicity, and evaluate the observed charge states in the absence and presence of detergents. Using ion mobility-mass spectrometry, we assess the proteins' stability as well as the ability to maintain non-covalent interactions with ligands. Finally, we examine lipid transfer from mixed detergent-lipid micelles containing the various detergents to soluble proteins. In summary, we found that C8E4 detergent reduces the proteins’ charge states, stabilizes the proteins and facilitates lipid transfer.