Adsorption of β-Hairpin Peptides on the Surface of Water:  A Neutron Reflection Study

Abstract

Neutron reflectivity has been used to determine the thickness and surface coverage of monolayers of two 14-residue beta-hairpin peptides adsorbed at the air/water interface. The peptides differed only in that one was labeled with a fluorophore, while the other was not. The neutron reflection measurements were mainly made in null reflecting water, NRW, containing 8.1% D(2)O. Under this isotopic contrast the water is invisible to neutrons and the specular signal was then only from the peptide layer. At the highest concentration of ca. 4 microg/mL studied, the area per peptide molecule (A) was found to be 230 +/- 10 and 210 +/- 10 A(2) for the peptides with and without a BODIPY-based fluorophore, respectively. The thickness of the peptide layers was about 10 A for a Gaussian distribution. With decreasing bulk peptide concentration, both surface excess and layer thickness showed a steady trend of decrease. While the neutron results clearly indicate structural changes within the peptide monolayers with increasing bulk concentration, the outstanding structural feature is the formation of rather uniform peptide layers, consistent with the structural characteristics typical of beta-strand peptide conformations. These structural features are well supported by the parallel measurements of the adsorbed layers in D(2)O. With this isotopic contrast the neutron reflectivity provides an estimate about the extent of immersion of the peptide layers into water. The results strongly suggest that the 14-mer peptide monolayers were fully afloat on the surface of water, with only the carboxy groups on Glu residues hydrated.

Interfacial assembly of proteins and peptides: recent examples studied by neutron reflection

“…It was further demonstrated that WWW15 could well form dimers through interdigitation of the two WWW sides, with the charged groups facing the negatively charged substrate and the aqueous solution. Neutron reflection has also been used to determine the adsorption of b hairpin peptides at the air-water interface using different ratios of H 2 O and D 2 O to highlight the layer differently (Lu et al 2003a). The peptides were found to form uniform layers of 8-10 Å , consistent with the formation of the single layer b sheet as predicted from computer modelling.…”

“…Neutron reflection is unique for revealing the structural features of peptide assembly at different interfaces and is highly complementary to other established techniques such as atomic force microscopy (AFM), circular dichroism and Fourier transform infrared (FTIR; Lu et al 2003aLu et al , 2004Zhao et al 2008bZhao et al , 2009). The technique has been used for characterizing interfacial adsorption from both biomimetic and designed peptides.…”

The interfacial structure and Young's modulus of peptide films having switchable mechanical properties

“…Although peptide adsorption at interfaces has been extensively researched (Middelberg et al 2000;Jones & Middelberg 2002b;Lu et al 2003Lu et al , 2004Sjogren & Ulvenlund 2004), only AM1 (Dexter et al 2006) has, to date, been reported to act as a switchable peptide surfactant. The surprising finding that AM1 could switch the stability of a foam or emulsion, in seconds and without a significant change in interfacial tension, stimulated us to characterize the interface using neutron reflectometry.…”

Nucleation of protein fibrillation by nanoparticles

“…These diseases involve self-assembly of soluble proteins into large insoluble fibrils through nucleation-dependent assembly, often via the formation of oligomeric structures that possess toxic properties (24,25). It has been shown that surfaces presented by lipid bilayers (26), collagen fibers (27), polysaccharides (28,29), and other liquid-air, liquid-solid, or liquidliquid interfaces (30,31) can have specific and significant effects in promoting amyloid formation. These observations suggest that interactions with different surfaces could promote protein self-assembly into amyloid fibrils and enhance protein conformational changes associated with other protein misfolding diseases.…”