Minkov Vasily S, Boldyreva Elena V
Novosibirsk State University , 2 Pirogov str., 630090 Novosibirsk, Russian Federation.
J Phys Chem B. 2014 Jul 24;118(29):8513-23. doi: 10.1021/jp503154x. Epub 2014 Jul 2.
Sulfhydryl groups play an important role in the formation of native structures of proteins and their biological functions. In the present work, we report for the first time the crystal structure of D,L-homocysteine and the results of a detailed study of the dynamics of its sulfhydryl group on cooling by precise single-crystal X-ray diffraction combined with polarized Raman spectroscopy of oriented single crystals. Although the crystal structures of both D,L-cysteine and D,L-homocysteine are layered, hydrogen bonds formed by -SH groups differ. In contrast with the crystal structure of D,L-cysteine with weak S-H · · · S hydrogen bonds between layers, D,L-homocysteine resembles the structures of amino acids with hydrophobic aliphatic side chains with no hydrogen bonds between the layers. The side chain of D,L-homocysteine forms a three-centered S-H · · · O hydrogen bond with carboxylate groups of two neighboring zwitterions. On cooling down, despite the shortening of the two S · · · O distances in the bifurcated S-H · · · O hydrogen bond, the wavenumber of the stretching vibrations of -SH groups increases. The same effect was also observed previously for other sulfhydryl containing amino acids, L-cysteine, and N-acetyl-L-cysteine on increasing pressure and is related to the strengthening of a three-centered bifurcated S-H · · · O hydrogen bond.
巯基在蛋白质天然结构的形成及其生物学功能中起着重要作用。在本研究中，我们首次报道了D,L-高半胱氨酸的晶体结构，以及通过精确的单晶X射线衍射结合取向单晶的偏振拉曼光谱对其巯基在冷却过程中的动力学进行详细研究的结果。虽然D,L-半胱氨酸和D,L-高半胱氨酸的晶体结构都是层状的，但由-SH基团形成的氢键有所不同。与层间具有弱S-H···S氢键的D,L-半胱氨酸晶体结构不同，D,L-高半胱氨酸类似于具有疏水脂肪族侧链的氨基酸结构，层间没有氢键。D,L-高半胱氨酸的侧链与两个相邻两性离子的羧基形成三中心S-H···O氢键。冷却时，尽管分叉的S-H···O氢键中的两个S···O距离缩短，但-SH基团伸缩振动的波数增加。之前在其他含巯基氨基酸、L-半胱氨酸和N-乙酰-L-半胱氨酸压力增加时也观察到了相同的效应，这与三中心分叉S-H···O氢键的加强有关。
