MULTIPLE CONFORMATIONAL STATES OF A PRO-PRO PEPTIDE - SOLID-STATE AND SOLUTION CONFORMATIONS OF BOC-AIB-PRO-PRO-NHME
MULTIPLE CONFORMATIONAL STATES OF A PRO-PRO PEPTIDE - SOLID-STATE AND SOLUTION CONFORMATIONS OF BOC-AIB-PRO-PRO-NHME
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DOI：
10.1021/ja00350a053
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发表时间：
1983-01-01
影响因子：
15
通讯作者：
BALARAM, P
中科院分区：
文献类型：
--
作者：
BALARAM, H;PRASAD, BVV;BALARAM, P
用X-射线衍射法和核磁共振研究了模型肽Boc-AIB-Pro-Pro-NHMe[Boc=叔丁氧羰基，AIB=α-氨基异丁酰基]的固相构象和溶液构象。该多肽在固体状态下采用多(Pro II)构象。在不对称单元中观察到两个分子，它们的氨酯基的几何构型(顺式/反式)不同。这些分子在晶体中通过一个复杂的氢键网络连接在一起，其中包括3个水分子，这些水分子共同结晶。单晶在低温下的溶解(apprx。233K)允许对固态构象进行核磁共振观察。在溶液中，该肽经历了Pro-Pro键的跨顺异构化。低温核磁共振测量允许检测Pro-Pro片段的3种构象状态。顺式和反式异构体都围绕着Cα-CO(.PSI.)Pro-3的键在低温下是可以检测到的。理论计算表明，对于.PSI，存在明显的活化势垒。旋转。NH化学位移的温度和溶剂依赖性提供了分子内氢键的证据，涉及顺式Pro-Pro构象中的NHMe基团。能量计算表明，有可能存在由4.fwdarw稳定的VI型β转角构象。1AIB-1CO和NHMe基团之间的氢键。
The solid-state and solution conformations of the model peptide Boc-Aib-Pro-Pro-NHMe [Boc = tert-butyloxycarbonyl, Aib = .alpha.-aminoisobutyryl] were studied by X-ray diffraction and NMR. The peptide adopts a poly(proline II) conformation in the solid state. Two molecules are observed in the asymmetric unit differing in the geometry (cis/trans) of the urethane group. The molecules are held together in the crystal by a complex network of H-bonds involving 3 molecules of water, which cocrystallize. Dissolution of single crystals at low temperature (.apprx. 233 K) permits NMR observation of the solid-state conformer. In solution, the peptide undergoes a trans-cis isomerization of the Pro-Pro bond. Low-temperature NMR measurements allow the detection of 3 conformational states of the Pro-Pro segment. Both cis'' and trans'' rotational isomers about the C.alpha.-CO (.psi.) bond of Pro-3 are detectable at low temperatures. Theoretical calculations suggest an appreciable activation barrier to .psi. rotation. Temperature and solvent dependence of NH chemical shifts provide evidence for an intramolecular H-bond, involving the NHMe group in the cis Pro-Pro conformer. Energy calculations suggest the possibility of a type VI .beta.-turn conformation stabilized by a 4 .fwdarw. 1 H-bond between the Aib-1 CO and NHMe groups.