SIDE CHAIN INTERACTIONS GOVERNING A-HELIX STABILITY

阿尔法障碍定位规则。 我们计划通过实验来确定 在未折叠多肽中控制α-螺旋位置的规则 链 与天然蛋白质的X射线结构相比， 显示这些规则是否也支配天然蛋白质中的螺旋位置。 的 计划是使用化学合成的肽（长度13-15个残基）， 目录侧链之间的特定相互作用， 使阿尔法螺旋在水中不稳定。 最近的研究表明， 核糖核酸酶A的C肽（残基1-13，终止于HSer-13内酯） 在0和20 ℃之间的水中确实显示部分螺旋形成（第一 Brown & Klee，Biochemistry 8，2876; 1971观察到），并且螺旋 稳定性强烈依赖于pH值，可能是因为盐桥Glu 9-...螺旋稳定性需要His 12+（Bierzynski，Kim & Baldwin， Proc. Natl. Acad. Sci. USA，in press，1982）. 我们会用化学方法 合成的肽来测试这种提出的相互作用， 研究C肽螺旋中其他可能的侧链相互作用 （一个可能的盐桥Glu 2-. Arg 10+，可能的疏水性 Phe-8环与Ala-4，Ala-5， Ala-6，或Phe-8和Ala-6侧链之间可能的疏水侧链 Lys-7和His-12的链）。 以这些结果为基础， 将继续测量螺旋稳定的自由能， 侧链相互作用，通过研究一系列化学合成的 肽，每个肽在一条侧链上不同于前面的肽 互动

Rules Governing Alpha-Helix Location. We plan to determine experimentally the rules governing a-helix location in an otherwise unfolded polypeptide chain. Comparison with the X-ray structures of native proteins then will show if these rules also govern helix location in native proteins. The plan is to use chemically synthesized peptides (length 13-15 residues) to catalogue specific interactions between side chains which stabilize or destabilize an Alpha-helix in water. Recent work has shown that the C-peptide of ribonuclease A (residues 1-13, terminating in HSer-13 lactone) does show partial helix formation in water between 0 and 20 C (first observed by Brown & Klee, Biochemistry 8, 2876; 1971) and that helix stability is strongly pH-dependent, probably because the salt bridge Glu 9-...His 12+ is needed for helix stability (Bierzynski, Kim & Baldwin, Proc. Natl. Acad. Sci. USA, in press, 1982). We will use chemically synthesized peptides to test this proposed interaction and also to investigate other possible side chain interactions in the C-peptide helix (a possible salt bridge Glu 2-...Arg 10+, a possible hydrophobic interaction between the Phe-8 ring and the side chains of Ala-4, Ala-5, Ala-6, or a possible hydrophobic side chain between Phe-8 and the side chains of Lys-7 and His-12). Starting from these results as a base, we will proceed to measure the free energy of helix stabilization for other side chain interactions, by studying a series of chemically synthesized peptides, each differing from a preceding peptide in one side chain interaction.