NTA-Ni lipids affect membrane phase behavior and fluorescence of lipid-like dyes

Abstract

The nitrilotriacetic acid group coordinated with nickel, NTA(Ni), is the standard chelator for purifying fusion proteins containing poly-histidine tags. The development of lipids with NTA(Ni) headgroups has enabled the specific attachment of His-tagged peptides and proteins to model membranes. Recently, these lipids have become essential for the study of surface-mediated protein phase separation and membrane interaction with biomolecular condensates. While this approach is gaining popularity, the intrinsic effects of NTA(Ni) lipids on the properties of the host membrane have been very little studied. As the field begins to unveil the mechanisms driving membrane-condensate interactions, decoupling the effects of the anchor lipid from those of the condensate is critical to avoid misinterpretations. Here, we systematically characterize model membranes containing 18:1 DGS-NTA(Ni), one of the most widely used chelator lipids. We evaluate its impact on fundamental membrane properties, including lipid packing, compressibility, and stability. Using Brewster Angle Microscopy (BAM), we investigate how DGS-NTA(Ni) modulates lipid phase separation. Finally, using fluorescence spectroscopy we address how nickel ion quenching influences the performance of lipid-like and solvatochromic dyes. Our results demonstrate that DGS-NTA(Ni) lipids have considerable effects on membrane properties and fluorescence of lipophilic dyes, which must be accounted for when interpreting the effect of his-tagged proteins attached to the membrane or membrane anchored condensates.