Conformation, Orientation, and Adsorption Kinetics of Dermaseptin B2 onto Synthetic Supports at Aqueous/Solid Interface

Abstract

The antimicrobial activity of cationic amphipathic peptides is due mainly to the adsorption of peptides onto target membranes, which can be modulated by such physicochemical parameters as charge and hydrophobicity. We investigated the structure of dermaseptin B2 (Drs B2) at the aqueous/synthetic solid support interface and its adsorption kinetics using attenuated total reflection Fourier transform infrared spectroscopy and surface plasmon resonance. We determined the conformation and affinity of Drs B2 adsorbed onto negatively charged (silica or dextran) and hydrophobic supports. Synthetic supports of differing hydrophobicity were obtained by modifying silica or gold with omega-functionalized alkylsilanes (bromo, vinyl, phenyl, methyl) or alkylthiols. The peptide molecules adsorbed onto negatively charged supports mostly had a beta-type conformation. In contrast, a monolayer of Drs B2, mainly in the alpha-helical conformation, was adsorbed irreversibly onto the hydrophobic synthetic supports. The conformational changes during formation of the adsorbed monolayer were monitored by two-dimensional Fourier transform infrared spectroscopy correlation; they showed the influence of peptide-peptide interactions on alpha-helix folding on the most hydrophobic support. The orientation of the alpha-helical Drs B2 with respect to the hydrophobic support was determined by polarized attenuated total reflection; it was around 15 +/- 5 degrees. This orientation was confirmed and illustrated by a molecular dynamics study. These combined data demonstrate that specific chemical environments influence the structure of Drs B2, which could explain the many functions of antimicrobial peptides.

Understanding protein adsorption phenomena at solid surfaces

“…If a protein is structurally stable its orientation on the surface can be characterized by 'side-on' or 'end-on' orientation, referring to an elliptically shaped particle that is respectively attached with its long or short axis to the surface [91][92][93]. Clearly, the final layer thickness of a protein monolayer in its saturation state is higher in the case of 'end-on' oriented proteins than in the case of 'side-on' oriented proteins which has been exploited by Lu et al [94][95][96][97] and Su et al [98][99][100].…”

“…On the one hand, some proteins or peptides exhibit their function only after adsorption [30,92]. By contrast, adsorption can also lead to the irreversible alteration of proteins that do not refold into their native structure after desorption.…”

“…The resonance frequency and the angle of reflection minimum depend on the boundary conditions of the interface. Thus, by measuring these parameters the layer thickness, the adsorbed amount, and density fluctuations can be determined which also allows to record protein adsorption kinetics [92,217]. However, SPR necessarily requires substrates coated with a metal layer which limits its versatility.…”

Plasticins: membrane-damaging peptides with ‘chameleon-like’ properties

“…Figure 3 illustrates the diversity of physico-chemical properties of the plasticin family in comparison with two members of the dermaseptin superfamily, dermaseptin B2 and dermaseptin S9. The three representative plasticins have identical overall hydrophobicities (0.39) and amphipathicities, corresponding to a hydrophobic sector that subtends a radial angle of 1808 on a helical wheel projection, in contrast to dermaseptin B2 [41,42] presenting a radial angle of 1208. Interestingly, dermaseptin S9 does not resemble any of the antimicrobial peptides identified to date, and in sharp contrast to known helical antimicrobial peptides, dermaseptin S9 has a highly hydrophobic core sequence comprising 10 bulky aliphatic and aromatic residues, which is flanked on either side by polar/ cationic residues [43].…”

“…The degree of perturbation is thus in part linked to peptide shape [60]. Like the dermaseptins S [12,14] and B [18,41], the dermatoxins [61], the phylloxins [62], and the phylloseptins [63], cationic plasticins are mainly helical when bound to anionic mimetic membranes but can also adopt alternative structural fittings including b-hairpin-like structures at this interface [21,22] (Table 2 and Figure 4). This is in contrast to the well-known antimicrobials, magainin and cecropin, that also adopt helical structures at an air-water interface, whereas melittin only adopts a helical structure in the presence of lipids [64].…”