Secondary conformation of short lysine‐ and leucine‐rich peptides assessed by optical spectroscopies: Effect of chain length, concentration, solvent, and time

Abstract

Solution secondary structures of three synthetic cationic peptides, currently used in antisense oligonucleotide delivery into living cells, have been analyzed by means of circular dichroism (CD) and Raman scattering in different buffers as a function of concentration and time. All three peptides are of minimalist conception, i.e., formed by only two types of amino acids (leucine: L and lysine: K). Two of these peptides contain 15 aminoacids: N(ter)- KLLKLLLKLLLKLLK (L(10)K(5)), N(ter)-KLKLKLKLKLKLKLK (L(7)K(8)), and the third one has only 9 residues: N(ter)-KLKLKLKLK (L(4)K(5)). The conformational behavior of the 15-mers in pure water differs considerably one from another. Although both of them are initially disordered in the 50-350 microM range, L(10)K(5) gradually undergoes a disordered to alpha-helix transition for molecular concentrations above 100 microM. In all other solvents used, L(10)K(5) adopts a stable alpha-helical conformation. In methanol and methanol/Tris mixture, nonnative alpha-helices can be induced in both KL-alternating peptides, i.e., L(7)K(8) and L(4)K(5). However, in major cases and with a time delay depending on peptide concentration, beta-like structures can be gradually formed in both solutions. In PBS and methanol/PBS mixture, the tendency for L(7)K(8) and L(4)K(5) is to form structures belonging to beta-family. A discussion has been undertaken on the effect of counterions as well as their nature in the stabilization of ordered structures in both KL-alternating peptides.

Vibrational Analysis of Amino Acids and Short Peptides in Hydrated Media. II. Role of KLLL Repeats To Induce Helical Conformations in Minimalist LK-Peptides

“…The conformational equilibrium shift observed in the 11-mer upon environmental change reveals again the influence of methanol as a solvent with a low dielectric constant, favoring the stabilization of intramolecular interactions and consequently helical conformers. 13,24 These solute-solvent interactions compensate, in evidence, the shortness of the 11-mer to adopt a stable helical conformation in phosphate buffer (only two complete R-helical turns are expected in this peptide). An excess of salt and especially that of Cl -anions might be responsible for a positive charge screening of lysine residues, presumably via interactions with water molecules, favoring a preferential formation of -strands.…”

Electronic circular dichroism and nuclear magnetic resonance studies of peptides derived from the FKBP52‐interacting β‐turn of the hERα ligand‐binding domain

“…The ECD spectrum of the synthetic peptide corresponding to the sequence K 362 RVPGFVDLTL 372 (Peptide 1 : Ac‐KRVPGFVDLTL‐NH 2 , Figure ) shows, at a concentration of ∼ 300 μM a major random coil contribution with a strong negative maximum at λ ∼ 198 nm ([θ] MRE ∼ −16 000 deg.cm 2 .dmol −1 .resid −1 , π → π* electronic transition). Additionally, the weak negative shoulder observed at λ ∼ 230 nm ([θ] MRE ∼ −2004 deg.cm 2 .dmol −1 .resid −1 ) could imply the presence of a turn conformation, outside the context of the folded protein . A shortened version of this peptide, which has previously been shown to interact with the FKBP52 FK1 domain (i.e., Peptide 2 : Ac‐RVPGFVD‐NH 2 ), shows about a 50% decrease of the signal intensity at ∼ 198 nm ([θ] MRE ∼ −8780 deg.cm 2 .dmol −1 .resid −1 ) whereas the shoulder at ∼ 230 nm increases slightly ([θ] MRE ∼ −2650 deg.cm 2 .dmol −1 .resid −1 ), as shown in Figure .…”

“…The secondary structure of the FKBP52‐binding peptide 6 was also observed to evolve as a function of the temperature (temperature gradient from 10 °C to 70 °C). The superimposed spectra show an isodichroic point at ∼205 nm, revealing two conformational populations, one of which most likely corresponds to a turn (Figure C) …”

Nanostructures from Single Amino Acid‐Based Molecules: Stability, Fibrillation, Encapsulation, and Fabrication of Silver Nanoparticles

“…As discussed earlier, the presence of KCl brings about the rupture of the vesicular structure, hence facilitating the release of the encapsulated drug. Moreover, we successfully transferred these nanovesicles into a biological buffer, such as PBS, in a bicomponent mixture with methanol44 at very low salt concentration (5 m M ), but the presence of high saline concentration of commonly used PBS solution leads to complete lysis of the drug‐loaded vesicular structure, which allows the release of drug into the surroundings (Supporting Information, Figure S18a–c), indicating a probable use of these nanovesicles as model study for carrying drugs. This phenomenon was further confirmed by UV absorption studies (Supporting Information, Figure 17c).…”

“…Methanolic solution (5 m M ) of peptide I was mixed with highly diluted phosphate buffer saline (PBS buffer containing 5 m M phosphate buffer, 0.1 m M KCl and 5 m M NaCl) maintaining the bicomponent mixture of methanol‐PBS (1:1)44 and SEM analysis carried out as before.…”