SIDE CHAIN INTERACTIONS GOVERNING A-HELIX STABILITY

管理Alpha-Helix位置的规则。我们计划通过实验确定 控制未折叠多肽中a-螺旋位置的规则 链条。与天然蛋白质的X-射线结构进行比较 展示这些规则是否也控制着天然蛋白质中的螺旋位置。这个 计划是使用化学合成的多肽(长度13-15个残基)来 编目稳定或稳定的侧链之间的特定相互作用 使水中的α-螺旋结构不稳定。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) 确实显示在0到20℃之间的水中形成了部分螺旋(第一 由Brown&Klee观察，《生物化学》，8,2876；1971)和螺旋 稳定性强烈地依赖于pH，可能是因为盐桥Glu 9-...他的12+是螺旋稳定所必需的(Bierzynski，Kim&Baldwin， 程序娜塔莉。阿卡德。SCI。美国，出版，1982)。我们将使用化学方法 合成多肽来测试所提出的相互作用，并 研究C-肽螺旋中其他可能的侧链相互作用 (可能是盐桥Glu 2-…Arg 10+，可能是疏水性的 Phe-8环与Ala-4，Ala-5， Ala-6，或Phe-8与侧链之间可能的疏水侧链 Lys-7和His-12链)。以这些结果为基础，我们 将继续测量其他分子螺旋稳定的自由能 侧链相互作用，通过研究一系列化学合成的 多肽，每个在一个侧链上不同于前一个多肽 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.