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

α螺旋是蛋白质中最重要的二级结构之一。这种结构的一个关键特征是在一个残基的C=O和另一个残基的NH之间形成氢键。虽然测量这种相互作用对我们理解氢键及其对螺旋整体稳定性的贡献很重要，但直接测量这种相互作用强度的工作却很少。在这个项目中，将进行一系列的实验来测量α螺旋中主链C=O to NH氢键的强度。在这些实验中，模型螺旋中一个残基的- nh2官能团被- ch2官能团取代。由于CH2基团的极性远低于NH基团，因此CH2不会形成氢键，因此这种变化有效地从整个螺旋结构中去除了单个氢键。这种修饰对螺旋结构的影响将使用圆二色性（CD）来监测。通过比较修饰肽和未修饰对照之间CD信号的强度，可以确定由于单氢键的去除而导致螺旋的丢失。使用一种叫做Lifson-Roig模型的统计力学处理；螺旋度的变化可以解释为由于缺乏单个残基-残基相互作用而造成的能量损失，从而测量缺失的氢键的强度。

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.