Gallay J, Vincent M, Nicot C, Waks M
Laboratoire pour l'Utilisation du Rayonnement Electromagnétique du Centre National de la Recherche Scientifique, Université Paris Sud, Orsay, France.
Biochemistry. 1987 Sep 8;26(18):5738-47. doi: 10.1021/bi00392a024.
The tryptophan (Trp) rotational dynamics and the secondary structure of the peptide hormones adrenocorticotropin-(1-24) [ACTH(1-24)]--the fully active N-terminal fragment of adrenocorticotropin-(1-39)--and glucagon were studied in aqueous solutions and in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/isooctane, a system selected to mimic the membrane-water interface. In aqueous solutions, the total fluorescence intensity decays of their single Trp residue [Trp-9 and Trp-25 for ACTH(1-24) and glucagon, respectively] are multiexponential. This is also the case for ACTH(5-10), a fragment of the adrenocorticotropin "message" region. Time-resolved fluorescence anisotropy data evidence a high degree of rotational freedom of the single Trp residue. Transfer of these peptides from water to the aqueous core of reverse micelles induces severe restrictions of the Trp internal motion and of its local environment. The results indicate that the Trp-9 residue in ACTH(1-24 is maintained in the close neighborhood of the water-AOT molecular interface where the water molecules are strongly immobilized. By contrast, the Trp residues in ACTH(5-10) and glucagon are likely to be located closer to the center of the micellar aqueous core where the water molecules are in a more mobile state. Furthermore, the above location of Trp can be extended to the peptide chains themselves as evidenced by the overall correlation time values of the peptide-containing micelles. Nevertheless, in all peptides, the indole ring remains susceptible to oxidation by N-bromosuccinimide. Circular dichroism measurements evidence the induction in glucagon of alpha-helices remaining unaffected by the micellar water content. Conversely, beta-sheet structures are favored in ACTH(1-24) at low water-to-surfactant molar ratios (w0) but are disrupted by subsequent additions of water. These results are discussed in terms of the possible role of the micellar interfaces in selecting the preferred peptide dynamical conformation(s)
研究了肽类激素促肾上腺皮质激素 -（1 - 24）[促肾上腺皮质激素（1 - 24）]——促肾上腺皮质激素 -（1 - 39）的完全活性 N 端片段——和胰高血糖素在水溶液以及双（2 - 乙基己基）磺基琥珀酸钠（AOT）/水/异辛烷的反胶束中的色氨酸（Trp）旋转动力学和二级结构，该体系被选来模拟膜 - 水界面。在水溶液中，它们单个 Trp 残基[促肾上腺皮质激素（1 - 24）和胰高血糖素分别为 Trp - 9 和 Trp - 25]的总荧光强度衰减是多指数的。促肾上腺皮质激素“信息”区域的片段促肾上腺皮质激素（5 - 10）也是如此。时间分辨荧光各向异性数据表明单个 Trp 残基具有高度的旋转自由度。这些肽从水转移到反胶束的水核中会导致 Trp 内部运动及其局部环境受到严重限制。结果表明，促肾上腺皮质激素（1 - 24）中的 Trp - 9 残基保持在水分子被强烈固定的水 - AOT 分子界面的紧邻区域。相比之下，促肾上腺皮质激素（5 - 10）和胰高血糖素中的 Trp 残基可能更靠近胶束水核的中心，那里的水分子处于更易移动的状态。此外，如含肽胶束的整体相关时间值所示，上述 Trp 的位置可以扩展到肽链本身。然而，在所有肽中，吲哚环仍易被 N - 溴代琥珀酰亚胺氧化。圆二色性测量表明，胰高血糖素中α - 螺旋的诱导不受胶束水含量的影响。相反，在低水与表面活性剂摩尔比（w0）时，促肾上腺皮质激素（1 - 24）中β - 折叠结构占优势，但随后加水会使其破坏。根据胶束界面在选择优选肽动态构象方面的可能作用对这些结果进行了讨论。
