Peptide-bicelle interaction: Following variations in size and morphology by a combined NMR-SAXS approach

• Published in: Biochimica et biophysica acta. Biomembranes Vol. 1862; no. 2; p. 183095
• Main Authors: F. Dudás, E., Wacha, A., Bóta, A., Bodor, A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-02-2020
• Subjects: Bicelle; Hydrodynamic radius; Lipid Bilayers - metabolism; Magnetic Resonance Spectroscopy - methods; Melitten - metabolism; Membrane protein; Membrane Proteins - metabolism; Micelles; Peptides - metabolism; PFG-NMR; SAXS; Scattering, Small Angle; X-Ray Diffraction - methods; DMPG; Membrane protein; Hydrodynamic radius; PFG-NMR; rH; Bicelle; DHPC; DMPC; SAXS
• ISSN: 0005-2736; 1879-2642
• DOI: 10.1016/j.bbamem.2019.183095

Changes in membrane properties occurring upon protein interaction are key questions in understanding membrane protein function. To report on the occurring size and shape variation we present here a combined NMR-SAXS method performed under physiological conditions using the same samples, enabling determination of a global parameter, the hydration radius (rH) and estimating the bicelle shape. We use zwitterionic (DMPC/DHPC) and negatively charged (DMPC/DHPC/DMPG) bicelles and investigate the interaction with model transmembrane and surface active peptides (KALP23 and melittin). 1H NMR measurements based mostly on the translational diffusion coefficient D determination are used to characterize cmc values of DHPC micelles under the investigated conditions, to describe DHPC distribution with exact determination of the q (long chain/short chain) lipid ratio, to estimate aggregation numbers and effective rH values. The scattering curve is used to fit a lenticular core-shell model enabling us to describe the bicelle shape in terms of ellipsoidal axis length parameters. For all studied systems formation of oblate ellipsoids is found. Even though the rG/rH ratio would be an elegant way to characterize shape variations, we show that changes occurring upon peptide-bicelle interaction in the “effective” size and in the measure on the anisometry - morphology - of the objects can be described by using rH and the simplistic ellipsoidal core-shell model. While the influence of the transmembrane KALP peptide is significant, effects upon addition of surface active melittin peptide seem negligible. This synergy of techniques under controlled conditions can provide information about bicellar shape modulation occurring during peptide-bicelle interactions.
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•A combined NMR-SAXS approach was tested for bicelles.•Size (rH) and shape (effective geometrical parameters) changes were monitored.•Bicelle solution composition was characterized (DHPC distribution, real q, Nagg).•For global characterization rH and effective geometrical parameters (SAXS) are useful.