Investigating the Lipid Selectivity of the Ammonium Transporter AmtB in Heterogeneous Nanodiscs

The structure and function of membrane proteins can be significantly impacted by the surrounding lipid environment, but membrane protein-lipid interactions in lipid bilayers are often difficult to study due to their transient and polydisperse nature. Here, we used two native mass spectrometry (MS) approaches to investigate how the Escherichia coli ammonium transporter (AmtB) selectively remodels its local lipid environment in heterogeneous lipoprotein nanodiscs. First, we used gas-phase ejection to isolate AmtB with bound lipids from heterogeneous nanodiscs with different combinations of lipids. Second, we used solution-phase detergent “flash” extraction as an orthogonal approach to study AmtB remodeling with native MS. Flash extraction of AmtB showed that Triton X-100 retains lipid selectivity, but C8E4 distorts preferential lipid interactions. Both approaches reveal that AmtB has a few tight binding sites for PC, is selective for binding PG overall, and is nonselective for PE, providing a detailed picture of how AmtB binds different lipid head groups in the context of mixed lipid bilayers. ### Competing Interest Statement The authors have declared no competing interest.