A simple model for the optical properties of chiral amides

Woody, Robert W.

doi:10.1002/bip.360220128

Cited by 16 publications

(6 citation statements)

References 42 publications

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“…However, the expected torsional angles in a-helical systems would not be expected to lead to large VCD. 31 An alternate source of monosignate VCD characteristic of a-helical structure could be amide-11-amide-I11 r n i~i n g .~~.~~ Since we have not been able to observe the amide-I11 VCD, we cannot evaluate the possibility of such a n occurrence. In principle, interaction of the local amide-I1 mode with any of the other amide modes could give rise to monosignate VCD.…”

Section: Amide I1mentioning

confidence: 97%

Vibrational circular dichroism of polypeptides. II. Solution amide II and deuteration results

Sen

Keiderling

1984

Biopolymers

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SynopsisVibrational CD (VCD) of amide I and I1 vibrations of several a-helical polypeptides have been measured in solution. For the amide I1 as well as the amide I [previously published: Lal, B.B. & Nafie, L.A. (1982) Biopolymers 21, 21611 we find the VCD to be characteristic of the polypeptide secondary structure. Amide I1 bands of right-handed u helices were all found to have negative VCD and to have their maximum rotational strength for the parallel (low-energy) component. However, left-handed a helices formed from L-amino acids gave positive amide I1 bands at higher frequencies than found for the right-handed helices, indicating that the VCD was sensitive to the stereochemical difference. The amide-I VCD spectra of some deuterated right-handed a-helical polypeptides have a new negative feature to low frequency that does not reflect theoretical predictions but also appears to be stereochemically sensitive. Amide-I1 and amide-A VCD of a few deuterated polypeptides imply retention of the secondary-structure-dependent characteristics seen in the hydrogenated VCD.

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Section: Amide I1mentioning

confidence: 97%

Vibrational circular dichroism of polypeptides. II. Solution amide II and deuteration results

Sen

Keiderling

1984

Biopolymers

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“…The VCD may also correlate to a twist of the , 4 structure over many subunits. 30 It is interesting to note that PLS, supposedly a random-coil exam~l e ,~~ gives VCD of the same magnitude and shape as do the heteroatom ,&sheet structures. It also has aP-type amide-I frequency of 1620 cm-'.…”

Section: Amide Imentioning

confidence: 99%

Vibrational circular dichroism of polypeptides. III. Film studies of several α‐helical and β‐sheet polypeptides

Sen

Keiderling

1984

Biopolymers

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SynopsisVibrational CD (VCD) of amides A, I, and I1 vibrations of a variety of polypeptide films have been measured. VCD of films of a-helical and /%sheet structures are compared in the three regions. Reproducible spectra could only be obtained for thin films free of orientation dependence. The sign and band shape of the VCD of films are not always the same as that in solution. However, the magnitude of the observed VCD seems to correlate with the secondary structure such that a-helical molecules typically have much larger A d c values than do ,@sheet molecules. The possibility of interference by artifacts owing to light-scattering effects is discussed.

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“…Keq may be varied in Equation 3 so that the correlation between the observed A E and that calculated with Equation 4 is maximal. Unfortunately, the molar CD coefficients are not known and cannot be reliably calculated based on structure because CD depends not only on the conformation of a peptide, but on its length (Chen et al, 1974), polarity of secondary structures with respect to each other (Chen et al, 1974), amino acid composition (Applequist, 1979a,b), side-chain conformation (Applequist, 1982), nonplanarity of the amide bond (Woody, 1983), and the presence of disulfides and aromatics (Labhardt, 1986). Therefore, experimental measures of the AE coefficients were desired.…”

Section: Calculation O F~g 'mentioning

confidence: 99%

Thermodynamics of melittin tetramerization determined by circular dichroism and implications for protein folding

Wilcox

Eisenberg

1992

Protein Science

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The tetramerization of melittin, a 26-amino acid peptide from Apis mellifera bee venom, has been studied as a model for protein folding. Melittin converts from a monomeric random coil to an a-helical tetramer as the pH is raised from 4.0 to 9.5, as ionic strength is increased, as temperature is raised or lowered from about 37 "C, or as phosphate is added. The thermodynamics of this tetramerization (termed "folding") are explored using circular dichroism. The melittin tetramer has two pK, values of 7.5 and 8. [7][8][9][10][11][12][13][14][15][16][17][18] agree with experimental titration data. Greater electrostatic repulsion of these protonated groups destabilizes the tetramer by 3.6 kcal/mol at pH 4.0 compared to pH 9.5. Increasing the concentration of NaCl in the solution from 0 to 0.5 M stabilizes the tetramer by 5-6 kcal/mol at pH 4.0. The effect of NaCl is modeled with a ligand-binding approach. The melittin tetramer is found to have a temperature of maximum stability ranging from 35.5 to 43 "C depending on the pH, unfolding above and below that temperature. AC; for folding ranges from -0.085 to -0.102 cal g" K-', comparable to that of other small globular proteins (Privalov, P.L., 1979, Adv. Protein Chem. 33, 167-241). A H o and ASo are found to decrease with temperature, presumably due to the hydrophobic effect (Kauzmann, w., 1959, Adv. Protein Chem.14, 1-63). Phosphate is found to perturb the equilibrium substantially with a maximal effect at 150 mM, stabilizing the tetramer at pH 7.4 and 25 "C by 4.6 kcal/mol. The enthalpy change due to addition of phosphate (-7.5 kcal/mol at 25 "C) can be accounted for by simple dielectric screening. Both circular dichroism and crystallographic results suggest that phosphate may bind Lys 23 at the ends of the elongated tetramer. These detailed measurements give insight into the relative importance of various forces for the stability of melittin in the folded form and may provide an experimental standard for future tests of computational energetics on this simple protein system. Abbreviations: CD, circular dichroism; far UV, 260-185 nm; near UV, 330-245 nm; AzgO, light absorption at 280 nm; AC:, the standard change in heat capacity from the unfolded to the folded form; At = AL -AR, where AL and AR are the absorbance of left and right circularly polarized light, respectively; AcZU, Ac at 222 nm; AtZB2, At at 282 nm; Th, a temperature at which AHo(T) = 0; T,, a temperature at gates to form an a-helical tetramer. The amount of tetwhich ASo( T ) = 0; TES, N-tris(hydroxyrnethyl)methyl-2-aminoethane sulfonic acid. Keywords

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A simple model for the optical properties of chiral amides

Cited by 16 publications

References 42 publications

Vibrational circular dichroism of polypeptides. II. Solution amide II and deuteration results

Vibrational circular dichroism of polypeptides. II. Solution amide II and deuteration results

Vibrational circular dichroism of polypeptides. III. Film studies of several α‐helical and β‐sheet polypeptides

Thermodynamics of melittin tetramerization determined by circular dichroism and implications for protein folding

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