Determination of Hydrogen Bond Strength in an Alpha-Helix by Replacement of Backbone Functional Groups

Black Hills State University, Spearfish SD

Investigators

Abstract

9986235 Zehfus The alpha helix is one of the most prominent secondary structures that appear in proteins. A key feature of this structure is a hydrogen bond that forms between the C=O of one residue and the NH of another residue four positions away in the sequence. While measuring this interaction is important to our understanding of both the hydrogen bond, and its contribution to the stability of the helix as a whole, little work has been done to measure directly the strength of this interaction. In this project a series of experiments will be carried out to measure the strength of the backbone C=O to NH hydrogen bond in an alpha helix. In these experiments the -NH- functional group of one residue in a model helix is replaced with a -CH2- functional group. Since the CH2 moiety is far less polar than the NH group, the CH2 will not form a hydrogen bond, so this change effectively removes a single hydrogen bond from the overall helix structure. The effect of this modification on the helix structure will be monitored using circular dichroism (CD). By comparing the strength of the CD signal between modified peptides and an unmodified control, it is possible to determine how helix is lost due to the removal of the single hydrogen bond. Using a statistical mechanical treatment called the Lifson-Roig model; the change in helicity can then be interpreted as the energy loss due to the absence of a single residue-residue interaction, thus measuring the strength of the missing hydrogen bond.