Folding of immunogenic peptide fragments of proteins in water solution. I. Sequence requirements for the formation of a reverse turn Article

Dyson, HJ, Rance, M, Houghten, RA et al. (1988). Folding of immunogenic peptide fragments of proteins in water solution. I. Sequence requirements for the formation of a reverse turn . JOURNAL OF MOLECULAR BIOLOGY, 201(1), 161-200. 10.1016/0022-2836(88)90446-9

cited authors

  • Dyson, HJ; Rance, M; Houghten, RA; Lerner, RA; Wright, PE

authors

abstract

  • A systematic examination by 1H nuclear magnetic resonance of the population of β-turn-containing conformers in several series of short linear peptides in water solution has demonstrated a dependence on amino acid sequence which has important implications for initiation of protein folding. The peptides consist of a number of variants of the sequence Tyr-Pro-Tyr-Asp, the trans isomer of which was previously shown to contain a reverse turn in water. Two-dimensional rotating-frame nuclear Overhauser effect spectroscopy provides unequivocal evidence that substantial populations of reverse turn conformations occur in water solutions of certain of these peptides. In the unfolded state, the peptides adopt predominantly extended chain (β) conformations in water. It appears probable from the nuclear Overhauser effect connectivities observed that the reverse turns in the trans isomers are predominantly type II. The low temperature coefficient of the amide proton resonance of the residue at position 4 of the turn suggests the presence of an intramolecular hydrogen bond. The presence of the β-turn conformation has been confirmed for certain peptides by circular dichroism measurements. Substitutions at positions 3 and 4 in the sequence Tyr-Pro-Tyr-Asp-Val can enhance or abolish the β-turn population in the trans peptide isomers. The residue at position 3 of the turn is the primary determinant of its stability. A small amount of additional stabilization appears to result from an electrostatic interaction between the side-chain of residue 4 and the unblocked amino terminus. For peptides of the series Tyr-Pro-X-Asp-Val, where X represents all l-amino acids except Trp and Pro, the temperature coefficient of the Asp4 amide proton resonance provides a measure of the β-turn population. The β-turn populations in water solution measured in this way correlate with the β-turn probabilities determined from protein crystal structures. This indicates that it is frequently the local amino acid sequence, rather than medium- to long-range interactions in the folded protein, that determines the β-turn conformation in the folded state. Such sequences are excellent candidates for protein folding initiation sites. A high population of structured forms appears to be present in the cis isomer of certain of the peptides, as shown by a considerable increase in the proportion of the cis isomer and by measurement of nuclear Overhauser effects and 3JNα coupling constants. The predominant structure appears to be a type VI β-turn, with cis-proline at position 3. Estimates of the β-turn population suggest that, in the most favourable peptides, as much as 70% of the cis isomer may exist in type VI turn conformations. The turn population for the trans peptides is smaller, but may be as high as 50% for certain peptides. The observed stability of β-turns in small peptide fragments of proteins suggests that turns are to be expected in polypeptide chains under folding conditions where they may have a profound influence on protein folding pathways. © 1988.

publication date

  • May 5, 1988

published in

Digital Object Identifier (DOI)

start page

  • 161

end page

  • 200

volume

  • 201

issue

  • 1