Transformation of the ϕ-ψ plot for proteins to a new representation with local helicity and peptide torsional angles as variables
✍ Scribed by Warner L. Peticolas; Beth Kurtz
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1980
- Tongue
- English
- Weight
- 635 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0006-3525
No coin nor oath required. For personal study only.
✦ Synopsis
Synopsis
A new representation of protein structure is obtained by the angular coordinate transformations 11; = (&+I -$i)/2 and [i = @;+I + with careful mathematical attention to the cyclical boundary conditions of all of the variables involved. From published 4-4 data it is possible to obtain a new ?-( plot. As the angle [; is varied from -180° through 0" to +180° in this plot, the local helicity of the polypeptide chain changes continuously and contiguously without sudden reversals in handedness. The variable, ti, gives the torsional position of the ith peptide group. Some peptide groups in proteins, such as the second peptide residue in a type I1 @-turn, are nonhydrogen-bonded and can undergo considerable torsional oscillation.
In such cases the 9 angle should be represented by a line whose length reflects the allowed dynamical variations in the peptide torsional position. Certain peptide residues in proteins may be able to undergo a complete torsional rotation of 360'. Such residues would be represented on the ?-[ plot as a straight line across the plot parallel to the abscissa. Other examples of the possible usefulness of this plot are also given.