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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Conformation Dependence of pK_a:Ab Initio and DFT Investigation of Histidine
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Conformation Dependence of pK_a:Ab Initio and DFT Investigation of Histidine

机译：pK_a：Ab从头构象依赖性和组氨酸的DFT研究

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摘要

Proton affinity and pK_a values of N-formyl-L-histidinamide are found to vary as a function of its backbone and/or side-chain orientation.Proton affinities between the cationic and neutral forms of structurally similar conformers are between-246 and-230 kcal mol~~(-1),while pK_a values associated with the same conformers are between 6 and 8.For the neutral-to-anion transition,the following ranges were computed-342>PA>-350 kcal mol~(-1)and 18 < pK_a < 22.The protonation state of histidines on the surface of a protein depends primarily on the pH.Due to protonation or deprotonation,the side-chain and/or backbone orientation of these histidine residues may undergo considerable changes.Examples are presented and confirmed by ab initio calculations,where proteins were crystallized under various pH conditions,resulting in the same histidine residue to adopt different conformations.Furthermore,a hypothesis is given for a protonation-induced conformational modification of the histidine residue in the catalytic triad of chymotrypsin during catalysis,which lowers the pK_a value of the catalytic histidine by 1.2 units.Both the experimental and theoretical results support that proton affinity as well as that pK_a values of histidine residues are strongly conformationally dependent.
机译：发现N-甲酰基-L-组氨酸酰胺的质子亲和力和pK_a值随其主链和/或侧链方向的变化而变化。结构相似构象的阳离子和中性形式之间的质子亲和力在-246和-230之间kcal mol ~~（-1），而与相同构象异构体相关的pK_a值在6和8之间。对于中性到阴离子的跃迁，计算出以下范围-342> PA> -350 kcal mol〜（-1 ）和18 K_a <22.蛋白质表面上组氨酸的质子化状态主要取决于pH值。由于质子化或去质子化，这些组氨酸残基的侧链和/或主链取向可能发生相当大的变化。提出并通过从头算来证实，其中蛋白质在各种pH条件下结晶，导致相同的组氨酸残基采用不同的构象。此外，给出了质子化诱导的组氨酸残基构象修饰的假设在胰凝乳蛋白酶的催化三联体中，催化组氨酸的pK_a值降低了1.2个单位。实验和理论结果均支持质子亲和力以及组氨酸残基的pK_a值都强烈依赖构象。

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