Conformation of MeAla6-cyclosporin A by NMR. Relationship of sidechain orientation of the MeBmt-1, MeLeu-9, and MeLeu-10 residues to immunosuppressive activity.

P R Gooley, P L Durette, J Boger, I M Armitage
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Abstract

MeAla6-cyclosporin A (MeAla6-CsA) is a unique CsA analog that shows weak immunosuppressive activity and yet binds strongly to the proposed cytosolic protein receptor, cyclophilin (CyP). Preliminary 1H NMR data showed significant chemical shift differences between spectra of MeAla6-CsA and CsA, suggesting different preferred conformations. A more detailed study, however, revealed that the backbone conformations of the two molecules are essentially identical, and that the differences can be accounted for, principally, by the sidechain motions of the MeBmt-1, MeLeu-9, and -10 residues. ROE and coupling constant data show that in MeAla6-CsA, the preferred chi 1 rotamers for MeLeu-9 and -10 are + 180 degrees (T), whereas in CsA there is a more even distribution of rotamer populations for MeLeu-10, and a preferred -60 degrees (G-) chi 1 rotamer for MeLeu-9. Similar data argue that the sidechain of MeBmt-1 is more restricted in its motion in MeAla-CsA than in CsA. Temperature studies suggest that these preferred rotamers for MeAla6-CsA may increase the stability of the hydrogen bond between NH(7) and CO(11), but prevent particular residues, especially the essential MeBmt-1 sidechain, from adopting orientations required to elicit immunosuppressive activity. The significant changes observed in the preferred orientations for the sidechains of the MeBmt-1, MeLeu-9, and MeLeu-10 residues in MeAla6-CsA argue that the particular orientations which they assume in CsA are not essential for cyclophilin binding.

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meala6 -环孢素A的NMR构象。MeBmt-1、MeLeu-9和MeLeu-10残基侧链取向与免疫抑制活性的关系
MeAla6-cyclosporin A (MeAla6-CsA)是一种独特的CsA类似物,显示出弱的免疫抑制活性,但与提出的细胞质蛋白受体亲环蛋白(CyP)结合强烈。初步的1H NMR数据显示MeAla6-CsA和CsA的光谱之间存在显著的化学位移差异,表明不同的优先构象。然而,一项更详细的研究表明,这两种分子的主链构象本质上是相同的,这种差异主要是由MeBmt-1、MeLeu-9和-10残基的侧链运动来解释的。ROE和耦合常数数据表明,在MeAla6-CsA中,MeLeu-9和-10的首选chi -1旋转体为+ 180度(T),而在CsA中,MeLeu-10的旋转体种群分布更为均匀,MeLeu-9的首选chi -1旋转体为-60度(G-)。类似的数据表明MeBmt-1的侧链在MeAla-CsA中的运动比在CsA中更受限制。温度研究表明,MeAla6-CsA的这些首选转子可能会增加nh7和CO 11之间氢键的稳定性,但会阻止特定残基,特别是必需的MeBmt-1侧链采用引发免疫抑制活性所需的取向。MeAla6-CsA中MeBmt-1、MeLeu-9和MeLeu-10残基侧链择优取向的显著变化表明,它们在CsA中所假定的特定取向对于亲环蛋白结合并不是必需的。
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