A pulsed field gradient NMR diffusion investigation of enkephalin peptide‐sodium dodecyl sulfate micelle association

Abstract

Pulsed field gradient NMR (PFG-NMR) diffusion experiments were used to investigate the binding of leucine and methionine enkephalin peptides to anionic sodium dodecyl sulfate (SDS) micelles. The study was undertaken to investigate the mechanism of interaction between enkephalin peptides and SDS micelles and to determine if NMR-derived association constants, K(eq), can predict the elution order in electrokinetic chromatography (EKC). In EKC, peptides are separated on the basis of their interactions with micelles. The Leu-enkephalin peptide-micelle association constant increased from 130 +/- 8 to 1459 +/- 57 and 1744 +/- 64 M(-1), respectively, when an Arg or Lys was added to the C-terminus. The association constant of Leu-enkephalinamide was approximately equal to that of Leu-enkephalin-Arg. Substitution of Phe4 with a Trp or Gly2 with an Ala in the Leu-enkephalin peptides also increased the micelle binding affinity. These results confirm that the interaction of Leu-enkephalin peptides with SDS micelles is largely electrostatic and that the non-polar amino acid side chains interact with the hydrophobic micelle core. The peptide-micelle association constants for the cationic Met-enkephalin peptides were also greater than their zwitterionic counterparts. For example, the Met-enkephalin K(eq) value was 162 +/- 9 M(-1), while the association constants for Met-enkephalin-Arg, Met-enkephalin-Lys, and Met-enkephalinamide were, respectively, 674 +/- 31, 426 +/- 23, and 453 +/- 27 M(-1). In both Met-enkephalin and Met-enkephalinamide, replacing Gly2 with an Ala did not significantly increase the association constant. These results confirm that with the Met-enkephalin peptides, there was little or no interaction of the amino acid side chains with the micelle core. For both the Leu-enkephalin and Met-enkephalin peptides, the association constants were consistent with EKC results, in that the peptides with smaller K(eq) values were found to elute before those with larger association constants.

Structural Basis for the Association of the Redox-sensitive Target of Rapamycin FATC Domain with Membrane-mimetic Micelles

“…Using a similar approach, the equilibrium constants for the association of different leucine-and methionine-enkephalin peptides (34) and of the tripeptide GHG (33) with SDS micelles had been determined. Calculating the reciprocal and dividing it by the aggregation number for SDS micelles (ϭ 51 (49)) gives the K d values for the association with SDS micelles, which range for the different leucine-enkephalin peptides from 0.385 to 0.008 mM and for the different methionine-enkephalin peptides from 0.754 to 0.029 mM.…”

“…K d Determination-The dissociation constant for oxidized and reduced y1fatc bound to DPC micelles was determined using an approach similar to the one described in previous studies (33,34). If the protein-micelle complex is on fast exchange on the diffusion time scale, the measured diffusion coefficient D is a weighted average given by: …”

“…To calculate the K d for the protein-micelle complex, f b,p was derived from the measured diffusion constants as described above (33,34). The concentration of free micelles was estimated in the following way.…”

Effect of pH on the Binding of Sodium, Lysine, and Arginine Counterions to l‐Undecyl Leucinate Micelles

“…Viscosity measurements were made on select solutions to confirm that the changes observed in the micelle diffusion coefficients resulted from changes in their hydrodynamic radii and not from increasing solution viscosity. NMR diffusion measurements were also used to investigate the effect of solution pH on the binding of cationic amino acids to the negatively charged und-Leu micelle surface [29][30][31][32][33][34]. The counterions investigated in this study were sodium (Na ? )…”

Matrix-assisted diffusion-ordered spectroscopy

“…A number of reports have demonstrated the use of diffusion NMR in studying how surfactants, such as SDS, can solubilise peptides, hydrophobic drugs and as controlled release scaffolds [50][51][52] . This concept has been thoroughly reviewed by Silber et al 53 and provides a good theoretical underpinning of the thermodynamics of the process and of the selection mechanism.…”