Design, Synthesis, and Characterization of 4-Ester CI2, a Model for Backbone Hydrogen Bonding in Protein α-Helices

• Published in: Journal of the American Chemical Society 2000-12, Vol.122 (49), p.12079-12082
• Main Authors: Beligere, Gangamani S, Dawson, Philip E
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja001648e

The total synthesis of proteins enables unnatural groups to be incorporated into proteins to understand the molecular basis of protein stability and function. Chymotrypsin inhibitor 2 (CI2), is a small 64 residue protein consisting of an α-helix sandwiched by four β-strands. To directly evaluate the role of backbone hydrogen bonding in α-helices, an array of four amide bonds that span the length of the α-helix have been replaced with ester bonds. Residues 13, 16, 19, and 22 have been substituted with α-hydroxy acids using solid-phase synthesis, and the peptides were assembled by conformationally assisted ligation. The resulting 4-ester CI2 is a functional protease inhibitor that is destabilized by 2.93 kcal/mol compared to the all-amide protein. This study demonstrates that the formation of multiple consecutive hydrogen bonds is not required for the folding of protein α-helices.