The α-helix to β-sheet transition in poly(l-lysine): Effects of anesthetics and high pressure

doi:10.1016/0167-4838(92)90394-S

Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology

Volume 1119, Issue 2, 26 February 1992, Pages 211-217

https://doi.org/10.1016/0167-4838(92)90394-S Get rights and content

Poly(l-lysine) exists in a random-coil formation at a low pH, α-helix at a pH above 10.6, and transforms into β-sheet when the α-helix polylysine is heated. Each conformation is clearly distinguishable in the amide-I band of the infrared spectrum. The thermotropic α-to-β transition was studied by using differential scanning calorimetry. At pH 10.6, the transition temperature was 43.5°C and the transition enthalpy was 170 cal/mol residue. At pH 11.85, the measurements were 36.7°C and 910 cal/mol residue, respectively. Volatile anesthetics (chloroform, halothane, isoflurane and enflurane) partially transformed α-helix polylysine into β-sheet. The transformation was reversed by the application of hydrostatic pressure in the range of 100–350 atm. Apparently, the α-to-β transition was induced by anesthetics through partial dehydration of the peptide side-chains (β-sheet surface is less hydrated than α-helix). High pressure reserved this process by re-hydrating the peptide. Because the membrane spanning domains of channel and receptor proteins are predominantly in the α-helix conformation, anesthetics may suppress the activity of excitable cells by transforming them into a less than optimal structure for electrogenic ion transport and neurotransmission. Proteins and lipid membranes maintain their structural integrity by interaction with water. That which attenuates the interaction will destabilize the structure. These data suggest that anesthetics alter macromolecular conformations essentially by a solvent effect, thereby destroying the solvation water shell surrounding macromolecules.

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Streaming potential and quartz crystal microbalance measurements, combined with all-atom molecular dynamics simulations, were used to study the pH dependency of the adsorption of two basic homopolypeptides, poly-L-lysine (PLL) and poly-L-arginine (PARG), on $α$ -quartz surface. We report that the observed adsorption behavior rises from an interplay of $i$ ) the change in the number of possible peptide-surface ion pairs between the charged moieties and $i i$ ) repulsive electrostatic interactions between the polypeptide molecules. For low pH values, polypeptide adsorption was strongest and stable monolayers were formed. However, electrostatic repulsion between the polypeptides led to a relatively low maximum surface coverage. On the other hand, higher pH led to more weakly bound, but significantly denser, peptide films with limited stability. Simulations indicate that electrostatic interactions are the main driving force for adsorption, while hydrogen bonding and non-specific interactions also contribute. Additionally, the important role of the counterions of the negatively charged quartz surface that form a positively charged ion adlayer is highlighted. Ion release of the condensed sodium ions at the charged surface occurs via displacement by polypeptide adsorption. The mechanisms revealed by this work provide systematic guidelines to engineering active surfaces of charged peptides with controlled surface coverage and reversible binding.
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Glycosylated threonine (Thr) is a structural motif found in seemingly disparate natural proteins from deep-sea collagen to mucins. Synthetic mimics of these important proteins are of great interest in biomedicine. Such materials also provide ready access to probe the contributions of individual amino acids to protein structure in a controlled and tunable manner. N-Carboxyanhydride (NCA) polymerization is one major route to such biomimetic polypeptides. However, challenges in the preparation and polymerization of Thr NCAs have impeded obtaining such structures. Here, we present optimized routes to several glycosylated and acetylated Thr NCAs of high analytical purity. Transition metal catalysis produced tunable homo-, statistical, and block-polypeptides with predictable chain lengths and low dispersities. We conducted structural work to examine their aqueous conformations and found that a high content of free OH Thr induces the formation of water-insoluble β-sheets. However, glycosylation appears to induce a polyproline II-type helical conformation, which sheds light on the role of glyco-Thr in rigid proteins such as mucins and collagen.
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A polylysine peptide formed by 30 L-lysine residues (Lys30) was also studied. Polylysine at high pH has been shown to have unprotonated sidechains and to adopt α-helical conformation [72,73]. These domains are expected to have low mechanical stabilities with smaller or no forces peak in their force-extension curves.
The role of hydrophobic and polar interactions in providing thermodynamic stability to folded proteins has been intensively studied, but the relative contribution of these interactions to the mechanical stability is less explored. We used steered molecular dynamics simulations with constant-velocity pulling to generate force-extension curves of selected protein domains and monitor hydrophobic surface unravelling upon extension. Hydrophobic contribution was found to vary between one fifth and one third of the total force while the rest of the contribution is attributed primarily to hydrogen bonds. Moreover, hydrophobic force peaks were shifted towards larger protein extensions with respect to the force peaks attributed to hydrogen bonds. The higher importance of hydrogen bonds compared to hydrophobic interactions in providing mechanical resistance is in contrast with the relative importance of the hydrophobic interactions in providing thermodynamic stability of proteins. The different contributions of these interactions to the mechanical stability are explained by the steeper free energy dependence of hydrogen bonds compared to hydrophobic interactions on the relative positions of interacting atoms. Comparative analyses for several protein domains revealed that the variation of hydrophobic forces is modest, while the contribution of hydrogen bonds to the force peaks becomes increasingly important for mechanically resistant protein domains.
Biocompatible antimicrobial electrospun nanofibers functionalized with ε-poly-L-lysine
2018, International Journal of Pharmaceutics
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ε-PL-loaded specimens showed the characteristic absorption bands at 1670 cm−1 and 1560 cm−1 were attributed to the stretching vibration band of CO in amide groups, and the bending variation of NH groups, respectively (Liang et al., 2014). These two amide absorption bands confirmed the existence of amide groups and correspond to the random coil conformation adopted by ε-PL at low pH (Chiou et al., 1992). The absorptions at 3245 cm−1 and 3080 cm−1 were attributed to the Fermi resonance generated from the frequency multiplication of the amide absorption band II and the stretching vibration of NH, respectively.
The antimicrobial polypeptide ε-poly(l-lysine) (ε-PL) was electrostatically incorporated to poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) electrospun nanofibers. ε-PL loading and distribution was assessed by infrared spectra, ζ-potential measurements and the primary amino reactive dye fluorescamine. Functionalized fibers with 485 ± 140 nm diameter, could be loaded with 0.57–0.74 g ε-PL (g dressing)⁻¹ that released at a constant rate of 5.4 ± 2.8 mg ε-PL (g dressing day)⁻¹. Such a dressings resulted in two orders of magnitude lower bacterial colonization than non-functionalized PAA-PVA after 14 days of incubation. Bacterial impairment was attributed to the damage of cell membranes and the formation of intracellular reactive oxygen species. ε-PL functionalized nanofibers did not display cytotoxicity to human corneal epithelial cells, HCEpC, in 24 h MTT assays. However, the viability of rapidly growing tumoral HeLa cells decreased >50% under the same conditions. The prepared biocompatible nanofibrous dressings with durable antibacterial activity show potential application as wound dressings and other biomedical uses.
Effect of peptide secondary structure on adsorption and adsorbed film properties on end-grafted polyethylene oxide layers
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Herein, 10 mM PB with 5 mM sodium sulfate, without pH adjustment, was used to prepare 5 mg ml−1 PLL stock solution. α-Helices were formed using well-established methods [64], where the stock solution was diluted (50×) and the pH adjusted to 10.6 (Fig. 1a). α-Helices in this solution were transformed to β-sheets using established methods [60], where the sample was heated at 70 °C for 50 min (Fig. 1a).
Poly-l-lysine (PLL), in α-helix or β-sheet configuration, was used as a model peptide for investigating the effect of secondary structures on adsorption events to poly(ethylene oxide) (PEO) modified surfaces formed using θ solvents. Circular dichroism results showed that the secondary structure of PLL persisted upon adsorption to Au and PEO modified Au surfaces. Quartz crystal microbalance with dissipation (QCM-D) was used to characterize the chemisorbed PEO layer in different solvents (θ and good solvents), as well as the sequential adsorption of PLL in different secondary structures (α-helix or β-sheet). QCM-D results suggest that chemisorption of PEO 750 and 2000 from θ solutions led to brushes 3.8 ± 0.1 and 4.5 ± 0.1 nm thick with layer viscosities of 9.2 ± 0.8 and 4.8 ± 0.5 cP, respectively. The average number of H₂O per ethylene oxides, while in θ solvent, was determined as ∼0.9 and ∼1.2 for the PEO 750 and 2000 layers, respectively. Upon immersion in good solvent (as used for PLL adsorption experiments), the number of H₂O per ethylene oxides increased to ∼1.5 and ∼2.0 for PEO 750 and 2000 films, respectively. PLL adsorbed masses for α-helix and β-sheet on Au sensors was 231 ± 5 and 1087 ± 14 ng cm⁻², with layer viscosities of 2.3 ± 0.1 and 1.2 ± 0.1 cP, respectively; suggesting that the α-helix layer was more rigid, despite a smaller adsorbed mass, than that of β-sheet layers. The PEO 750 layer reduced PLL adsorbed amounts to ∼10 and 12% of that on Au for α-helices and β-sheets respectively. The PLL adsorbed mass to PEO 2000 layers dropped to ∼12% and 4% of that on Au, for α-helix and β-sheet respectively. No significant differences existed for the viscosities of adsorbed α-helix and β-sheet PLL on PEO surfaces. These results provide new insights into the fundamental understanding of the effects of secondary structures of peptides and proteins on their surface adsorption.
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Protein adsorption at the biomaterial–tissue interface is of utmost importance to the widespread application of engineered materials. The present study asked what role the secondary structures of peptides play in their adsorption, as well as how these structures affect the physicochemical properties of the final adsorbed layer. To this end, α-helices and β-sheets were induced in poly-l-lysine, and their adsorption to Au surfaces was monitored using quartz crystal microbalance with dissipation. It was observed that secondary structures played an important role in governing both the adsorption process and the final film properties. Higher initial adsorption rates were obtained for α-helices compared with β-sheets, regardless of solution salt concentration. Adsorption half-time for β-sheets was greater than that for α-helices, and the final amount adsorbed on β-sheet was significantly higher than that on α-helix. The adsorbed amount and adsorption half-time decreased with increasing salt concentration, suggesting that electrostatic interactions played a role. It was found that the differences in Zeta potential coupled with the apparent effect of surface contact area differences between α-helix and β-sheet conformations are ultimately responsible for these different peptide adsorption behaviours at the Au interface. The initial adsorption rate of α-helix increased with salt concentrations up to 50 mM, whereas β-sheet initial adsorption rates increased with salt concentrations up to 500 mM. Viscosities for films formed from α-helices were about twice those of β-sheets films, regardless of solution ionic strength. It was evident that the peptide secondary structures influence all aspects of their adsorption, as well as affecting the adsorbed film properties.

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The α-helix to β-sheet transition in poly(l-lysine): Effects of anesthetics and high pressure

Biochim. Biophys. Acta

Biochim. Biophys. Acta

Biochim. Biophys. Acta

J. Biol. Chem.

J. Colloid Interface Sci.

J. Colloid Interface. Sci.

Alcohol

Arch. Biochem. Biophys.

J. Cell Comp. Physiol.

J. Cell Comp. Physiol.

J. Cell Comp. Physiol.

Science

Anesthesiology

Anesthesiology

Anesthesiology

Biochem. J.

Anesthesiology

Anesthesiology

Chem. Rev.

Mol. Pharmacol.

J. Med. Chem.

J. Amer. Chem. Soc.

J. Amer. Chem. Soc.