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NMR spectroscopy techniques can provide important information about protein‐ligand interactions. Here we tested an NMR approach which relies on the measurement of paramagnetic relaxation enhancements (PREs) arising from analogous cationic, anionic or neutral soluble nitroxide molecules, which distribute around the protein‐ligand complex depending on near‐surface electrostatic potentials. We applied this approach to two protein‐ligand systems, interleukin‐8 interacting with highly charged glycosaminoglycans and the SH2 domain of Grb2 interacting with less charged phospho‐tyrosine tripeptides. The electrostatic potential around interleukin‐8 and its changes upon binding of glycosaminoglycans could be derived from the PRE data and confirmed by theoretical predictions from Poisson‐Boltzmann calculations. The ligand influence on the PREs and NMR‐derived electrostatic potentials of Grb2 SH2 was localized to a narrow protein region which allowed the localization of the peptide binding pocket. Our analysis suggests that experiments with nitroxide cosolutes can be useful for investigating protein‐ligand electrostatic interactions and mapping ligand binding sites. [ABSTRACT FROM AUTHOR]

The plasma membrane is a complex assembly of proteins and lipids that can self‐assemble in submicroscopic domains commonly termed "lipid rafts", which are implicated in membrane signaling and trafficking. Recently, photo‐sensitive lipids were introduced to study membrane domain organization, and photo‐isomerization was shown to trigger the mixing and de‐mixing of liquid‐ordered (lo) domains in artificial phase‐separated membranes. Here, we synthesized globotriaosylceramide (Gb3) glycosphingolipids that harbor an azobenzene moiety at different positions of the fatty acid to investigate light‐induced membrane domain reorganization, and that serve as specific receptors for the protein Shiga toxin (STx). Using phase‐separated supported lipid bilayers on mica surfaces doped with four different photo‐Gb3 molecules, we found by fluorescence microscopy and atomic force microscopy that liquid disordered (ld) domains were formed within lo domains upon trans‐cis photo‐isomerization. The fraction and size of these ld domains were largest for Gb3 molecules with the azobenzene group at the end of the fatty acid. We further investigated the impact of domain reorganization on the interaction of the B‐subunits of STx with the photo‐Gb3. Fluorescence and atomic force micrographs clearly demonstrated that STxB binds to the lo phase if Gb3 is in the trans‐configuration, whereas two STxB populations are formed if the photo‐Gb3 is switched to the cis‐configuration highlighting the idea of manipulating lipid‐protein interactions with a light stimulus. [ABSTRACT FROM AUTHOR]

NMR spectroscopy techniques can provide important information about protein-ligand interactions. Here we tested an NMR approach which relies on the measurement of paramagnetic relaxation enhancements (PREs) arising from analogous cationic, anionic or neutral soluble nitroxide molecules, which distribute around the protein-ligand complex depending on near-surface electrostatic potentials. We applied this approach to two protein-ligand systems, interleukin-8 interacting with highly charged glycosaminoglycans and the SH2 domain of Grb2 interacting with less charged phospho-tyrosine tripeptides. The electrostatic potential around interleukin-8 and its changes upon binding of glycosaminoglycans could be derived from the PRE data and confirmed by theoretical predictions from Poisson-Boltzmann calculations. The ligand influence on the PREs and NMR-derived electrostatic potentials of Grb2 SH2 was localized to a narrow protein region which allowed the localization of the peptide binding pocket. Our analysis suggests that experiments with nitroxide cosolutes can be useful for investigating protein-ligand electrostatic interactions and mapping ligand binding sites., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The plasma membrane is a complex assembly of proteins and lipids that can self-assemble in submicroscopic domains commonly termed "lipid rafts", which are implicated in membrane signaling and trafficking. Recently, photo-sensitive lipids were introduced to study membrane domain organization, and photo-isomerization was shown to trigger the mixing and de-mixing of liquid-ordered (l o ) domains in artificial phase-separated membranes. Here, we synthesized globotriaosylceramide (Gb 3 ) glycosphingolipids that harbor an azobenzene moiety at different positions of the fatty acid to investigate light-induced membrane domain reorganization, and that serve as specific receptors for the protein Shiga toxin (STx). Using phase-separated supported lipid bilayers on mica surfaces doped with four different photo-Gb 3 molecules, we found by fluorescence microscopy and atomic force microscopy that liquid disordered (l d ) domains were formed within l o domains upon trans-cis photo-isomerization. The fraction and size of these l d domains were largest for Gb 3 molecules with the azobenzene group at the end of the fatty acid. We further investigated the impact of domain reorganization on the interaction of the B-subunits of STx with the photo-Gb 3 . Fluorescence and atomic force micrographs clearly demonstrated that STxB binds to the l o phase if Gb 3 is in the trans-configuration, whereas two STxB populations are formed if the photo-Gb 3 is switched to the cis-configuration highlighting the idea of manipulating lipid-protein interactions with a light stimulus., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Dynamic structural transitions within the seven-transmembrane bundle represent the mechanism by which G-protein-coupled receptors convert an extracellular chemical signal into an intracellular biological function. Here, the conformational dynamics of the neuropeptide Y receptor type 2 (Y2R) during activation was investigated. The apo, full agonist-, and arrestin-bound states of Y2R were prepared by cell-free expression, functional refolding, and reconstitution into lipid membranes. To study conformational transitions between these states, all six tryptophans of Y2R were 13 C-labeled. NMR-signal assignment was achieved by dynamic-nuclear-polarization enhancement and the individual functional states of the receptor were characterized by monitoring 13 C NMR chemical shifts. Activation of Y2R is mediated by molecular switches involving the toggle switch residue Trp281 6.48 of the highly conserved SWLP motif and Trp327 7.55 adjacent to the NPxxY motif. Furthermore, a conformationally preserved "cysteine lock"-Trp116 23.50 was identified., (© 2020 The Authors. Published by Wiley-VCH GmbH.)