Helical peptides with three pairs of Asp‐Arg and Glu‐Arg residues in different orientations and spacings

Abstract

The helix-stabilizing effects of repeating pairs of Asp-Arg and Glu-Arg residues have been characterized using a peptide system of the same design used earlier to study Glu-Lys . The consequences of breaking ion pair and charge-helix dipole interactions by titration to pH 2 have been compared with the results of screening these interactions with NaCl at pH 7.0 and pH 2.5. The four peptides in each set contain three pairs of acidic (A) and basic (B) residues spaced either i, i + 4 or i, i + 3 apart. In one peptide of each kind the pairwise order of residues is AB, with the charges oriented favorably to the helix macrodipole, and in the other peptide the order is BA.The results are as follows: (1) Remarkably, both Asp-Arg and Glu-Arg peptides show the same pattern of helix stabilization at pH 7.0 found earlier for Glu-Lys and Asp-Lys peptides:The ion pairs and charge-helix dipole interactions cannot be cleanly separated, but the results suggest that both interactions make important contributions to helix stability. Because the four peptides of each set have nearly identical compositions, the large differences in helix content within each set cannot be caused by differences in length and sequence. (3) Significant differences in helix content remain at 5 M NaCI, where ion pair interactions are completely screened. The residual interactions may either be nonscreenable H-bond interactions or remaining charge-helix dipole interactions. Keywords: a-helices; charge-helix dipole interaction; ion pairsThe four Glu-Lys and the two Asp-Lys peptides studied by Baldwin (1987, 1990) have nearly the same amino acid compositions (the 16-and 17-residue peptides differ by one alanine residue) and yet show very different helix contents, both at pH 7.0 and at pH 2.5. Consequently, ion pair interactions and charge-helix dipole interactions make important contributions to helical stability. Since the initial report by Marqusee and Baldwin (1987), several other groups have demonstrated the importance of electrostatic interactions in the stability of a-helical peptides. Merutka and Stellwagen (1991) have investigated the effects of different acidic (A) and basic (B) residues on the stability of a peptide related to Marqusee and Baldwin's i + 4 AB. Gans et al. (1991) demonstrated, by using peptides comprised of only 8 Glu and

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

“…The effect of salt in the case of the (i, i + 3) and (i, i + 4) spacings is different: high salt favors helicity in the former case. Later work on peptides containing Asp-Arg pairs showed precisely the same order of stabilization as a function of spacing and order (Huyghues-Despointes et al, 1993a). The effect of order of the charged groups is consistent with a helix dipole interaction, as seen by Ihara et al (1982) as well, although in principle, other factors might be involved.…”

The role of context on α‐helix stabilization: Host‐guest analysis in a mixed background peptide model

“…Salt bridges between E and K have a stabilizing contribution to the formation of a-helix (Marqusee et al, 1987;Merutka & Stellwagen, 1991;Lyu et al, 1992a;Huyghues-Despointes et al, 1993). In our peptides, there are potentially seven pairs of salt bridges between E and K side chains.…”

“…3 positions. Although the former are not expected to have significant interactions, the latter can (Huyghues-Despointes et al, 1993). However, the use of charged residues cannot be completely avoided, otherwise solubility and aggregation problems may arise.…”

Dynamic charge interactions create surprising rigidity in the ER/K α-helical protein motif

“…The enhanced ␣-helical content of alanine peptides with occasional E, R, or K has been attributed to their ability to sequester water from the carbonyl oxygen and amide hydrogen groups in the ␣-helical backbone (4,9). Experiments examining sparse E-K interactions in alanine ␣-helices suggest that E-K charge interactions do not augment ␣-helical content relative to alanine ␣-helices with only one of E, R, or K (10,13,15).…”