A mass spectrometry-based approach to distinguish annular and specific lipid binding to membrane proteins

Membrane proteins engage in a variety of contacts with theirsurrounding lipids, but distinguishing between specifically boundlipids, and non-specific annular interactionsis a challenging problem. Applying native mass spectrometry to three membrane protein complexes with different lipid binding properties, we explore the ability of detergents to compete with lipids bound in different environments. We show that lipids in annular positions on the Presenilin Homologue protease are subject to constant exchange with detergent. Bycontrast,detergent-resistantlipids bound at the dimer interface in the Leucine transportershowdecreased koffrates in molecular dynamics simulations.Turning tothe lipid flippase MurJ, we findthat addition of the natural substrate lipid-II results in the formation of a 1:1 protein-lipid complex, where the lipid cannot be displaced by detergentfromthe highly protected active site.In summary, we distinguish annular from non-annular lipids based on their exchange rates in solution. [Abstract copyright: © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.