Intrinsic flexibility and structural adaptability of Plasticins membrane-damaging peptides as a strategy for functional versatility

The Plasticins are a family of antimicrobial, 23-29-residue Gly-Leu-rich ortholog peptides from the frog skin that have very similar amino acid sequences, hydrophobicities, and amphipathicities but differ markedly in their conformational plasticity and spectrum of activity. The intrinsic flexibility and structural malleability of Plasticins modulate their ability to bind to and disrupt the bilayer membranes of prokaryotic and eukaryotic cells, and/or to reach intracellular targets, therefore, triggering functional versatility. The discussion is opened herein on several examples of other membrane-active peptides, like viral fusion peptides, cell-penetrating peptides, that are able to display antimicrobial activity. Hence, Plasticins could be regarded as models of multipotent membrane-active peptides guided by structural plasticity.

Structural malleability of plasticins: Preorganized conformations in solution and relevance for antimicrobial activity

Plasticins (23 long-residue glycine-leucine-rich dermaseptin-related peptides produced by the skin of South American hylids) have very similar amino acid sequences, hydrophobicities, and amphipathicities, but differ in their membrane-damaging properties and structurations (i.e. destabilized helix states, beta-hairpin, beta-sheet, and disordered states) at anionic and zwitterionic membrane interfaces. Structural malleability of plasticins in aqueous solutions together with parameters that may govern their ability to fold within beta-hairpin like structures were analyzed through circular dichroism and FTIR spectroscopic studies completed by molecular dynamics simulations in polar mimetic media. The goal of this study was to probe to which extent pre-existent peptide conformations, i.e. intrinsic "conformational landscape", may be responsible for variability in bioactive conformation and antimicrobial/hemolytic mechanisms of action of these peptides in relation with their various membrane disturbing properties. All plasticins present a turn region that does not always result in folding into a beta-hairpin shaped conformation. Residue at position 8 plays a major role in initiating the folding, while position 12 is not critical. Conformational stability has no major impact on antimicrobial efficacy. However, preformed beta-hairpin in solution may act as a conformational lock that prevents switch to alpha-helical structure. This lock lowers the antimicrobial efficiency and explains subtle differences in potencies of the most active antimicrobial plasticins.

Conformation, orientation, and adsorption kinetics of dermaseptin B2 onto synthetic supports at aqueous/solid interface

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.

A possible role of the Na(+)/K(+)-ATPase for O(2) production from H(2)O(2)

We are attempting to supply a new insight on interaction between Na(+)/K(+)-ATPase and H(2)O(2). We demonstrate that in vitro the Na(+)/K(+)-ATPase, a non heme-protein, is able to disproportionate H(2)O(2) catalatically into dioxygen and water, as well as C(40) catalase. By polarography, we quantify O(2) production and by Raman spectroscopy H(2)O(2) consumption. A comparative analysis of kinetics parameters relative to O(2) production shows that for Na(+)/K(+)-ATPase the affinity of the catalytic site able to transform H(2)O(2) into O(2) is twice weaker than that for C(40) catalase. It also shows that the molar activity for O(2) production is 300-fold weaker for ATPase than for catalase. Inhibitors, pH and GSH studies highlight the differences between the heme- and nonheme-proteins. Indeed, for C(40), NaN(3) is strongly inhibiting, but much less for ATPase. The pH range for the catalatic activity of ATPase is wide (6.5 to 8.5), while it is not for C(40) catalase (optimum at pH 8). The Na(+)/K(+)-ATPase catalatic activity is reduced in presence of glutathione, while it is not the case with C(40) catalase.

Copper-adenine catalyst for O(2) production from H(2)O(2)

In solutions of CuCl2 and adenine copper can be bound to adenine. Two Cu(adenine)(2) complexes [Cu(C(5)H(5)N(5))(2)]2+/Cu(C(5)H(4)N(5))(2)] are in equilibrium with free adenine. Copper-adenine complexes present a catalytic activity (e.g., H(2)O(2) disproportionation into O(2) and water) but depending on complex concentration H(2)O(2) also strongly oxidizes the adenine within the complexes. Raman spectroscopy quantifies copper-adenine complex formation and H(2)O(2) consumption; polarography quantifies O(2) production. As for C(40) catalase, optimal catalytic capacities depend on physiological conditions, such as pH and temperature. The comparative analysis of kinetic parameters shows that the affinity for H(2)O(2) of Cu(adenine)(2) is 37-fold lower than that of C(40) catalase and that the molar activity for O(2) production is 200-fold weaker for Cu(adenine)(2) than for the enzyme. In the 10(-6)-10(-3) M range, the strong decrease of activity with raising complex concentration is explained by aggregation or stacking, which protects Cu(adenine)(2) entities from H(2)O(2) oxidation, but also decreases O(2) production.