Position dependence of the 13C chemical shifts of alpha-helical model peptides. Fingerprint of the 20 naturally occurring amino acids.
Position dependence of the 13C chemical shifts of alpha-helical model peptides. Fingerprint of the 20 naturally occurring amino acids.
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α-螺旋模型肽的 13C 化学位移的位置依赖性。
DOI：
10.1110/ps.04930804
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
Scheraga,HaroldA
中科院分区：
文献类型：
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作者：
Vila,JorgeA;Baldoni,HectorA;Scheraga,HaroldA
在由序列 Ac-(Ala)i-X-(Ala)j-NH2 表示的 α-螺旋模型肽的密度泛函水平上研究了 13C 化学位移的位置依赖性，其中 X 代表 20 种天然存在的氨基酸中的任何一种，其中 0 ≤ i≤ 8 且 i+j= 8。采用局部致密基础方法进行量子化学计算使我们能够减少 化学位移计算，同时保持结果的良好准确性。对于 α 螺旋中的 20 个天然存在的氨基酸，(1) 作为客体残基 (X) 和序列位置的函数，计算出的 13C 屏蔽存在显着变化；例如，在 N 末端，13Cα 和 13Cβ 屏蔽相对于中心或 C 末端位置表现出均匀的变化模式； (2) 螺旋内部的 13Cα 和 13Cβ 化学位移与计算值和观测值吻合良好，相关系数分别为 0.98 和 0.99；对于在螺旋中部计算的 13Cα 化学位移，只有 5 个残基（即 Asn、Asp、Ser、Thr 和 Leu）表现出超出观察到的标准偏差的化学位移； (3) 这些残基中的四个（Asn、Asp、Ser 和 Thr）仅对于 N 末端 13 Cα 化学位移的计算值有更好的一致性。结果表明，13Cβ（而非 13Cβ）化学位移足够敏感，足以反映某些氨基酸相对于肽和蛋白质的 N 和 C 末端在 α 螺旋内特定位置的倾向。
The position dependence of the13C chemical shifts was investigated at the density functional level for α‐helical model peptides represented by the sequence Ac‐(Ala)i‐X‐(Ala)j‐NH2, where X represents any of the 20 naturally occurring amino acids, with 0 ≤i≤ 8 andi+j= 8. Adoption of thelocally densebasis approach for the quantum chemical calculations enabled us to reduce the length of the chemical‐shift calculations while maintaining good accuracy of the results. For the 20 naturally occurring amino acids in α‐helices, there is (1) significant variability of the computed13C shielding as a function of both the guest residue (X) and the position along the sequence; for example, at the N terminus, the13Cαand13Cβshieldings exhibit a uniform pattern of variation with respect to both the central or the C‐terminal positions; (2) good agreement between computed and observed13Cαand13Cβchemical shifts in the interior of the helix, with correlation coefficients of 0.98 and 0.99, respectively; for13Cαchemical shifts, computed in the middle of the helix, only five residues, namely Asn, Asp, Ser, Thr, and Leu, exhibit chemical shifts beyond the observed standard deviation; and (3) better agreement for four of these residues (Asn, Asp, Ser, and Thr)onlyfor the computed values of the13Cαchemical shifts at the N terminus. The results indicate that13Cβ, but not13Cβ, chemical shifts are sensitive enough to reflect the propensities of some amino acids for specific positions within an α‐helix, relative to the N and C termini of peptides and proteins.