Interaction of guanidinium and ammonium cations with phosphatidylcholine and phosphatidylserine lipid bilayers – Calorimetric, spectroscopic and molecular dynamics simulations study

Phase-Dependent Adsorption of Myelin Basic Protein to Phosphatidylcholine Lipid Bilayers

“…When heated up to 50 • C, these features approach each other, resulting in one broad envelope with two maxima at 1466 cm −1 and 1455 cm −1 . As expected, in the examined spectral range, DPPC displays a band originating from γCH 2 with a maximum at 1468 cm −1 /1467 cm −1 at 20 • C/50 • C, along with two weak maxima at 1452 cm −1 and 1444 cm −1 at 20 • C due to the wagging progression of methylene groups (δCH 2 ) that disappear upon heating [59]. Additionally, a very weak feature on the high-frequency side of γCH 2 at 20 • C becomes more prominent at 50 • C and absorbs at 1479 cm −1 .…”

“…However, as a careful inspection of even raw spectra can unravel certain molecular-level details, the analysis of baseline-corrected and smoothed spectral data was performed. Therefore, obtained spectra were examined in the following spectral ranges: (i) 2890–2820 cm −1 , in which both antisymmetric (ν as CH 2 ) and symmetric (ν s CH 2 ) stretching of methylene groups of DPPC hydrocarbon chains appear, (ii) 1800–1480 cm −1 , in which the band originating from carbonyl stretching of lipid glycerol backbone (νC=O(OR)) appears, along with Amide I ((νC=O(NH)),) and Amide II (δNH)) bands of MBP [ 35 ], (iii) 1490–1430 cm −1 , which contains the signatures of DPPC methylene groups scissoring (γCH 2 ) and the bending of protonated amino moiety (δNH 3 + ) of MBP [ 59 ], (iv) 1335–1275 cm −1 comprising Amide III signature dominated by the bending of secondary amine (δN–H) coupled with stretching of CN (νC–N) and bending of CH (δCH) moiety of MBP [ 60 , 61 ], (v) 1275–1190 cm −1 , which reveals the signatures of phosphate moieties of lipid polar headgroups (ν as PO 2 − ) and bending of secondary amine (δN–H) coupled with stretching of CN moiety (νC–N) and bending of CH moiety (δCH) [ 60 ] of MBP, and (vi) 1015–935 cm −1 containing the signature of a choline group of lipid molecules (ν (a)s C–N(CH 3 ) 3 + ) [ 62 , 63 ]. In the selected ranges, the spectra were smoothed (Savitzky–Golay procedure using the polynomial of a 3rd degree through 10/40 points (256/128 scans) and baseline-corrected (2 points at spectral minima) [ 54 ].…”

Adsorption/Desorption of Cationic-Hydrophobic Peptides on Zwitterionic Lipid Bilayer Is Associated with the Possibility of Proton Transfer

“…Solutions of R5F2/K5F2 and suspensions DPPC ± R5F2/K5F2 were pipetted directly on the ATR crystal unit in a volume of 30 µL and their spectra were acquired against air as a background. Using OPUS 8.5 SPI (20200710) software, all spectra were collected at a nominal resolution of 2 cm −1 and 256 scans at two different temperatures, 30 • C and 50 • C, at which DPPC is either in a gel (30 • C) or fluid (50 • C) phase [21]. FTIR spectra of the solutions of R5F2/K5F2 and suspensions DPPC ± R5F2/K5F2 were acquired three times, whereas the PB solution was measured once.…”

“…Following the subtraction of the PB spectrum from R5F2/K5F2 and DPPC ± R5F2/K5F2 spectra acquired at the same temperature, the obtained difference FTIR spectra were examined in the following spectral regions: (i) 3000-2820 cm −1 , (ii) 1780-1695 cm −1 , (iii) 1515-1360 cm −1 , (iv) 1275-1190 cm −1 , (v) 1130-1020 cm −1 and (vi) 990-940 cm −1 , which display the bands originated from: (i) (anti)symmetric stretching of methylene moieties (ν (a)s CH 2 ) and those of methyl moieties (ν as CH 3 ), (ii) carbonyl stretching of glycerol backbone (νC=O), (iii) scissoring of methylene groups (γCH 2 ), symmetric stretching of carboxylic groups (ν s COO − ) and bending of protonated amino moiety (δNH 3 + ) of K5F2, (iv) antisymmetric stretching of phosphate groups and glycerol moieties (ν as PO 2 − and ν (a)s C−O), (v) symmetric stretching of phosphate and their neighboring C−O groups (ν s PO 2 − and ν s C−O) and (vi) antisymmetric stretching/bending modes of choline moieties (ν as N(CH 3 ) 3 + /δ as N(CH 3 ) 3 + ) (the vibrational bands assignment was made following the references [21,[35][36][37][38][39][40]). After selecting the listed spectral regions, FTIR spectra in the selected spectral ranges (regions except for (i)) were smoothed (Savitzky-Golay; polynomial of a 3rd degree through 20 points [31]), baseline corrected (two points) and normalized [31].…”

“…Since R5F2 is among the most potent CPP species, we sought to elucidate not only their adsorption mechanism on the DPPC lipid bilayer, but also the adsorption mechanism of the K5F2 peptide (Figure 1). Although the latter peptide was not the subject of research in the context of CPPs, the general importance of K-based peptides is not only evident from the cited literature, but also from our previous study of the adsorption of guanidinium (Gdm + ) and ammonium (NH 4 + ) cations, as model amino acids R and K, on zwitterionic and anionic lipid bilayers, which showed that proton-transfer is one of the key differences in their adsorption mechanism [21]. Regarding the choice of lipids, we focused on DPPC, which at experimentally attainable temperatures can be found in the gel phase (L β ), the ripple phase (P β ) and the fluid phase (L α ).…”