Woods R Jeremy, Brower Justin O, Castellanos Elena, Hashemzadeh Mehrnoosh, Khakshoor Omid, Russu Wade A, Nowick James S
Department of Chemistry, University of California-Irvine, Irvine, CA 92697-2025, USA.
J Am Chem Soc. 2007 Mar 7;129(9):2548-58. doi: 10.1021/ja0667965. Epub 2007 Feb 13.
The development of peptide beta-hairpins is problematic, because folding depends on the amino acid sequence and changes to the sequence can significantly decrease folding. Robust beta-hairpins that can tolerate such changes are attractive tools for studying interactions involving protein beta-sheets and developing inhibitors of these interactions. This paper introduces a new class of peptide models of protein beta-sheets that addresses the problem of separating folding from the sequence. These model beta-sheets are macrocyclic peptides that fold in water to present a pentapeptide beta-strand along one edge; the other edge contains the tripeptide beta-strand mimic Hao [JACS 2000, 122, 7654] and two additional amino acids. The pentapeptide and Hao-containing peptide strands are connected by two delta-linked ornithine (deltaOrn) turns [JACS 2003, 125, 876]. Each deltaOrn turn contains a free alpha-amino group that permits the linking of individual modules to form divalent beta-sheets. These "cyclic modular beta-sheets" are synthesized by standard solid-phase peptide synthesis of a linear precursor followed by solution-phase cyclization. Eight cyclic modular beta-sheets 1a-1h containing sequences based on beta-amyloid and macrophage inflammatory protein 2 were synthesized and characterized by 1H NMR. Linked cyclic modular beta-sheet 2, which contains two modules of 1b, was also synthesized and characterized. 1H NMR studies show downfield alpha-proton chemical shifts, deltaOrn delta-proton magnetic anisotropy, and NOE cross-peaks that establish all compounds but 1c and 1g to be moderately or well folded into a conformation that resembles a beta-sheet. Pulsed-field gradient NMR diffusion experiments show little or no self-association at low (</=2 mM) concentrations. Changes to the residues in the Hao-containing strands of 1c and 1g improve folding and show that folding of the structures can be enhanced without altering the sequence of the pentapeptide strand. Well-folded cyclic modular beta-sheets 1a, 1b, and 1f each have a phenylalanine directly across from Hao, suggesting that cyclic modular beta-sheets containing aromatic residues across from Hao are better folded.
肽β-发夹的开发存在问题，因为折叠取决于氨基酸序列，序列的改变会显著降低折叠率。能够耐受此类变化的稳定β-发夹是研究涉及蛋白质β-折叠片层的相互作用以及开发这些相互作用抑制剂的有吸引力的工具。本文介绍了一类新的蛋白质β-折叠片层的肽模型，该模型解决了折叠与序列分离的问题。这些模型β-折叠片层是大环肽，在水中折叠后沿一条边缘呈现一个五肽β-链；另一条边缘包含三肽β-链模拟物郝[《美国化学会志》2000年，122卷，7654页]和另外两个氨基酸。五肽链和含郝肽链通过两个δ-连接的鸟氨酸（δOrn）转角相连[《美国化学会志》2003年，125卷，876页]。每个δOrn转角都含有一个游离的α-氨基，允许单个模块连接形成二价β-折叠片层。这些“环状模块化β-折叠片层”通过线性前体的标准固相肽合成，然后进行溶液相环化来合成。合成了八个基于β-淀粉样蛋白和巨噬细胞炎性蛋白2序列的环状模块化β-折叠片层1a - 1h，并通过1H NMR进行了表征。还合成并表征了含有两个1b模块的连接环状模块化β-折叠片层2。1H NMR研究显示了低场α-质子化学位移、δOrn δ-质子磁各向异性以及NOE交叉峰，这些结果表明除了1c和1g之外，所有化合物都适度或良好地折叠成类似于β-折叠片层的构象。脉冲场梯度NMR扩散实验表明，在低（≤2 mM）浓度下几乎没有或没有自缔合现象。对1c和1g含郝肽链中的残基进行改变可改善折叠，这表明在不改变五肽链序列的情况下可以增强结构的折叠。折叠良好的环状模块化β-折叠片层1a、1b和1f在郝的正对面各有一个苯丙氨酸，这表明在郝的正对面含有芳香族残基的环状模块化β-折叠片层折叠得更好。
