THEORETICAL-STUDY OF BLOCKED GLYCINE AND ALANINE PEPTIDE ANALOGS
THEORETICAL-STUDY OF BLOCKED GLYCINE AND ALANINE PEPTIDE ANALOGS
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DOI：
10.1021/ja00016a010
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发表时间：
1991-07-31
影响因子：
15
通讯作者：
POPLE, JA
中科院分区：
文献类型：
--
作者：
HEADGORDON, T;HEADGORDON, M;POPLE, JA
我们提出了一个高层次的从头计算模型封闭的丙氨酸和甘氨酸二肽分子，（S）-α-（甲酰氨基）丙酰胺和α-（甲酰氨基）乙酰胺的研究。在HF/3- 21 G水平上对每个分子的常规定义的构象空间变量phi和psi的完全松弛网格进行了评价。为了获得目前可行的最佳结果，对于在HF/3- 21 G网格上观察到的所有最小值和过渡结构，获得了HF/6-31+G* 完全优化的几何构型和频率，并使用MP2/6-31+G**/HF/6-31+G* 单点能量计算探索了相关校正。HF/3- 21 G结构与大基的结果相当一致，尽管相对能量有时很差。在更高层次的理论，我们没有发现在区域中的最小值，ψ空间对应于蛋白质的二级结构，虽然这些区域是相对较低的能量。我们报告的存在下，在某些地区的放松（φ，psi）映射的两个系统的尖点，表面是双值在这些地区，和尖点发生的两个表面的能量交叉。我们还观察到显着偏差肽平面（高达40度）在几个地区的（φ，psi）地图。不连续性和大的肽扭曲表明（phi，psi）自由度本身并不能完全定义这些二肽分子的可用构象空间。最后，我们讨论了丙氨酸和甘氨酸之间的差异的分子起源完全放松（φ，psi）表面，差异是定性的Ramachandran地图推断一致。
We present a high-level ab initio study of the model blocked alanine and glycine dipeptide molecules, (S)-alpha-(formylamino)propanamide and alpha-(formylamino)ethanamide. Fully relaxed grids of the conventionally defined conformational space variables phi and psi have been evaluated for each molecule at the HF/3-21G level. In order to obtain the best results currently feasible, HF/6-31+G* fully optimized geometries and frequencies were obtained for all minima and transition structures observed on the HF/3-21G grid, and correlation corrections were explored with MP2/6-31+G**//HF/6-31+G* single-point energy calculations. The HF/3-21G structures are in reasonable agreement with the results of the larger basis, although the relative energies are sometimes poor. At the higher level of theory, we do not find minima in the regions of phi, psi-space corresponding to protein secondary structures, although these regions are relatively low in energy. We report the presence of a cusp in certain regions of the relaxed (phi,psi) map of both systems; the surfaces are double-valued in these regions, and the cusp occurs where the energies of the two surfaces cross. We also observe significant deviations from peptide planarity (up to 40-degrees) in several regions of the (phi,psi) map. The discontinuities and large peptide distortions indicate that the (phi,psi) degrees of freedom alone do not fully define the available conformational space of these dipeptide molecules. Finally we discuss the molecular origin of the differences between the alanine and glycine fully relaxed (phi,psi) surfaces, differences which are qualitatively consistent with those inferred from Ramachandran maps.