The Supporting Information, these data are also presented as the dependence in the imply residue ellipticity at 222 nm around the concentration of SDS. Within a buffer containing 150 mM NaCl (as in comparison to 15 mM), we observed comparable ellipticity adjustments occurring now at a 839712-12-8 Formula decrease concentration of SDS, in agreement with all the known reduce CMC for SDS at a salt concentration of 150 mM18,19 (Figure 1B of the Supporting Info). These final results help the assertion that the formation of micelles and not just the concentration of SDS will be the critical factor for induction of an R-helical conformation in the peptide. We have also examined the potential with the peptides to adopt an R-helical conformation inside the presence of trifluoroethanol (TFE), which has the ability to stabilize an R-helical conformation of peptides. In aqueous TFE options, each Ac1-18 and Ac1-18P are similarly capable to form R-helices in a TFE concentration-dependent manner (Figure 1B), indicating that phosphorylation will not impact the R-helical propensity of the peptide inside a hydrophobic TFE environment. We also investigated whether or not the potential in the peptides to form an R-helix in the presence of micelles depends upon the ionic nature in the headgroup of the detergent. Using CD spectroscopy, we examined the structures of Ac1-18 and Ac1-18P inside the presence of dodecylphosphocholine (DPC), dodecyl -Dglucoside (DG), or dodecyltrimethylammonium bromide (DTAB) micelles, which possess the same 12-carbon aliphatic tail as SDS but possess a zwitterionic, nonionic, or cationic headgroup, respectively, in location with the anionic headgroup of SDS. In the presence of four mM DPC (CMC = 1.1), we observed a dramatic increase inside the R-helical content material of Ac1-18 comparable to that in the presence of SDS micelles (Figure 2A). However, the helical content material of Ac1-18P within the presence of DPC was considerably decreased in comparison with that of Ac1-18 (Figure 2A). Thus, phosphorylation at Ser5 interferes with the induction of an R-helical conformation within the peptide inside the presence of zwitterionic DPC micelles, although to a lesser degree than inside the presence of anionic SDS micelles. The potential of Ac118 to form an R-helix within the presence of DPC is constant with preceding data displaying that in contrast to the key binding through the annexin A1 core, which features a strict requirement for anionic phospholipids, the secondary binding by way of the N-terminal tail can take place with each anionic and zwitterionic phospholipids.20-22 In the presence of 0.25 mM DG (CMC = 0.19 mM), both peptides have a mainly random-coil conformation (Figure 2B). Similarly, within the presence of 30 mM octyl -D-glucoside (CMC = 25 mM), an additional detergent with a nonionic headgroup, we did not observe important changes in the structure from the peptides (data notARTICLEFigure 2. Effect of Ser5 phosphorylation around the structure of the Ac1-18 peptide inside the presence of dodecylphosphocholine, dodecyl -D-glucoside, or dodecyltrimethylammonium bromide. CD spectra of 20 M Ac1-18 or Ac1-18P within the presence or absence of (A) 4 mM dodecylphosphocholine (DPC), (B) 0.25 mM dodecyl -D-glucoside (DG), or (C) 15 mM dodecyltrimethylammonium bromide (DTAB).shown). In the presence of 15 mM DTAB (CMC = 14.six mM), we could obtain CD spectra only above 215 nm, because of the higher absorbance and/or scatter of DTAB micelles under 215 nm. The values of mean residue ellipticities at 222 nm for both Ac1-18 and Ac1-18P increased considerably upon addition of DTAB (Figure 2C), comparable to.
