Periodic properties of proton conformational shifts in isolated protein helices: An experimental study

Abstract

In this work, the helix‐forming residues in fragments of several proteins (ribonuclease, thermolysin, tendamistat and angiogenin) were identified by NOE and the helix proton shifts were measured as δ changes associated with helix‐population increments driven by trifluoroethanol addition. When estimated in this way, a regular pattern of helix conformational shifts was clearly seen in the Δδ versus sequence profiles of all the peptides studied. The helix periodicity of the Hα and Hβ resonances was especially clear, an observation that earlier statistical studies of protein δ values failed to predict. Amide protons showed the largest helix shifts, but with a less‐sharply defined periodic character. Aromatic residues considerably distorted the periodicity of the helix amide shifts in some peptides, as evidenced by the δ shifts of a RNase A fragment 1–15 analog in which the two aromatic residues were replaced by Ala. The relationship between helix periodicity and peptide amphiphatic character is discussed. Copyright © 1992, Wiley Blackwell. All rights reserved