Diffusion NMR study of complex formation in membrane-associated peptides.

Area of Science:

• Biophysical Chemistry
• Materials Science
• Biochemistry

Background:

• Understanding peptide-surfactant interactions is crucial for drug delivery and biomaterial design.
• Sodium dodecyl sulfate (SDS) is a common surfactant used to solubilize and study peptides.
• Pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is a powerful technique for measuring diffusion and determining the size of molecular assemblies.

Purpose of the Study:

• To determine the hydrodynamic size of GAD-2 peptide complexes with SDS micelles using PFG-NMR.
• To investigate how SDS concentration affects the size and structure of GAD-2-SDS complexes.
• To compare the behavior of GAD-2 with smaller dipeptides in SDS solutions.

Main Methods:

• Utilized PFG-NMR to simultaneously measure diffusion coefficients of peptides and SDS.
• Applied a two-species model to analyze diffusion data as a function of SDS concentration.
• Calculated the hydrodynamic size and fraction of free SDS in GAD-2-SDS systems.

Main Results:

• At SDS concentrations ≤ 25 mM, a stable GAD-2-SDS complex with a hydrodynamic size of 5.5 ± 0.3 nm was observed.
• Between 25 mM and 60 mM SDS, the apparent complex size increased significantly, suggesting an increased number of peptides per complex.
• Self-diffusion coefficients of SDS differed with and without buffer at low concentrations but converged at higher concentrations.

Conclusions:

• PFG-NMR can accurately determine peptide-surfactant complex size at low SDS concentrations (≤ 25 mM).
• Higher SDS concentrations lead to complex structural changes, likely involving aggregation of GAD-2 peptides.
• Experimental conditions, particularly SDS concentration, are critical for obtaining reliable hydrodynamic size data of peptide-surfactant complexes.