Amodeo P, Saviano G, Borin G, Calderan A, Ruzza P, Tancredi T
Istituto per la Chimica di Molecole di Interesse Biologico, Consiglio Nazionale delle Ricerche, Arco Felice, Italy.
J Pept Res. 1998 Mar;51(3):180-7. doi: 10.1111/j.1399-3011.1998.tb01214.x.
To investigate the conformational flexibility of metal-complexed cyclodecapeptides, we synthesized and studied two antamanide analogs, in which the phenylalanine residue in position 6 or 9 of the sequence was substituted by Gly. Previous conformational studies on antamanide suggested that these backbone regions are affected by conformational variation. The NMR conformational study showed a high degree of flexibility for the two analogs. With sodium ions, on the other hand, [Gly9]-antamanide was able to form a fairly stable equimolar complex, whereas [Gly6]-antamanide showed a conformational heterogeneity, with one prevailing conformer. For the [Gly9]-antamanide analog, the whole NMR data, combined with extensive theoretical calculations, were consistent with the presence of 1) two beta-turns of type I, centered on Gly9-Phe10 and Ala4-Phe5, respectively; 2) a central cavity with a six-carbonyl oxygen cage, optimal for a Na+ hexacoordination; 3) strongly H-bonded amide protons for residues 1 and 6, both involved in the formation of the two type I beta-turns, which, however, exhibited some fluctuations during the molecular dynamics simulations. For the [Gly6]-antamanide-Na+ complex the prevailing conformer was consistent with a more open structure, with the partial solvent exposure of all the amide protons; that is, the Gly residue in position 6 increases the flexibility of this critical site more than does the Gly in position 9. These data in some way parallel the results of the cytotoxicity tests on B16-F10 transformed cells for the two analogs: [Gly9]-antamanide is cytotoxic after 48 h exposure, whereas [Gly6]-antamanide is almost inactive. On the contrary, both analogs are practically inactive in vivo against phalloidin.
为了研究金属络合环十肽的构象灵活性，我们合成并研究了两种抗毒环肽类似物，其中序列中第6位或第9位的苯丙氨酸残基被甘氨酸取代。先前对抗毒环肽的构象研究表明，这些主链区域会受到构象变化的影响。核磁共振构象研究表明这两种类似物具有高度的灵活性。另一方面，对于钠离子，[Gly9]-抗毒环肽能够形成相当稳定的等摩尔络合物，而[Gly6]-抗毒环肽则表现出构象异质性，其中一种构象占主导。对于[Gly9]-抗毒环肽类似物，整个核磁共振数据与广泛的理论计算相结合，与以下情况一致：1）分别以Gly9-Phe10和Ala4-Phe5为中心的两个I型β-转角；2）一个具有六羰基氧笼的中心腔，最适合钠离子的六配位；3）参与形成两个I型β-转角的残基1和6的酰胺质子形成强氢键，然而，在分子动力学模拟过程中，这些氢键表现出一些波动。对于[Gly6]-抗毒环肽-钠离子络合物，占主导的构象与更开放的结构一致，所有酰胺质子部分暴露于溶剂中；也就是说，第6位的甘氨酸残基比第9位的甘氨酸残基更能增加这个关键位点的灵活性。这些数据在某种程度上与这两种类似物对B16-F细胞的细胞毒性测试结果相似：[Gly9]-抗毒环肽在暴露48小时后具有细胞毒性，而[Gly6]-抗毒环肽几乎没有活性。相反，两种类似物在体内对抗鬼笔环肽几乎都没有活性。 10转化
