Peptide Orientation at Emulsion Nanointerfaces Dramatically Different from Flat Surfaces

Abstract

The adsorption of protein to nanoparticles plays an important role in toxicity, food science, pharmaceutics, and biomaterial science. Understanding how proteins bind to nanophase surfaces is instrumental for understanding and, ultimately, controlling nanoparticle (NP) biochemistry. Techniques probing the adsorption of proteins at NP interfaces exist; however, these methods have been unable to determine the orientation and folding of proteins at these interfaces. For the first time, we probe in situ with sum frequency scattering vibrational spectroscopy the orientation of model leucine-lysine (LK) peptides adsorbed to NPs. The results show that both α-helical and β-strand LK peptides bind the particles in an upright orientation, in contrast to the flat orientation of LKs binding to planar surfaces. The different binding geometry is explained by Coulombic forces between peptides across the particle volume.

Lysozyme Interaction with Phospholipid Nanodroplets Probed by Sum Frequency Scattering Vibrational Spectroscopy

“…In the SFG spectra, two features were fit between 1660 and 1685 cm –1 , assigned to high α-helical content (the most predominate feature) and protein aggregation, respectively. , In contrast to the SFS spectra, here, the predominant feature that relates the lysozyme to a phospholipid nanoparticle is the peak near 1685 cm –1 , suggesting that the bound lysozyme is also aggregated to a higher degree than for the case at the air–water interface. Of course, this is only one possibility, as we have previously found that small peptides bound to nanoparticles can adopt very different orientations due to extra Coulombic forces by lysozymes on the opposite side of the nanoparticle, which are absent in the case of planar air–water interfaces . Here, the comparison between the lipid nanoparticle and lipid planar surface is only an estimate as the subtraction method we employed to extract the amide I spectra can distort the peak shapes obtained.…”

“…Of course, this is only one possibility, as we have previously found that small peptides bound to nanoparticles can adopt very different orientations due to extra Coulombic forces by lysozymes on the opposite side of the nanoparticle, which are absent in the case of planar air−water interfaces. 29 Here, the comparison between the lipid nanoparticle and lipid planar surface is only an estimate as the subtraction method we employed to extract the amide I spectra can distort the peak shapes obtained. Furthermore, the orientation and structure of a protein at an interface gives rather unique spectra, and for the case of planar SFG, various methods to calculate experimental spectra have be developed to extract such information.…”

“…Sum frequency scattering (SFS) vibrational spectroscopy can overcome these limitations and is truly ideal to provide this information and is a powerful technique that is capable to provide surface molecular structure of lipid nanosurfaces. SFS is a vibrational coherent surface spectroscopy that provides information on molecular order, orientation, and chemical composition of interfacial molecules located on nanoparticles − and has been previously used to investigate the assembly of model peptides at nanosurfaces . Here, for the first time, we will use SFS to follow the interaction of the antimicrobial enzyme lysozyme with the surface of a solid lipid nanoparticle.…”

“…We first monitor the stability and any changes in particle size using dynamic light scattering (DLS). Then, using previously published SFS methods, ,, we use vibrations of the acyl chains of the phospholipids as reporters of structural ordering of the hydrophobic part of the lipid nanoparticle. Vibration assigned to the phosphate headgroup reports back on the structure change of the outermost nanoparticle surface.…”

“…SFS is a vibrational coherent surface spectroscopy that provides information on molecular order, orientation, and chemical composition of interfacial molecules located on nanoparticles 19−28 and has been previously used to investigate the assembly of model peptides at nanosurfaces. 29 Here, for the first time, we will use SFS to follow the interaction of the antimicrobial enzyme lysozyme with the surface of a solid lipid nanoparticle. Hen egg white lysozyme (HEWL, from now on referred to as lysozyme) is chosen as a model protein because it has been used to study protein corona formation due to its well-known characteristics and stability over a wide range of conditions.…”