Srikrishnan T, Parthasarathy R
Center for Crystallographic Research, Roswell Park Memorial Institute, Buffalo, New York.
Int J Pept Protein Res. 1987 Oct;30(4):557-63. doi: 10.1111/j.1399-3011.1987.tb03365.x.
Crystals of L-leucylglycylglycylglycine, LGGG (C12H22N4O5), grown from an ethanol-water solution, are orthorhombic, space groups P2(1)2(1)2(1), with unit cell dimensions (at 22 +/- 3 degrees) a = 9.337(1), b = 10.995(1), c = 15.235(1)A, v = 1563.4 A3, Z = 4 with a density of Dobs = 1.29 g.cm-3 and Dcalc = 1.279 g.cm-3. The crystal structure was solved by the application of direct methods and refined to an R value of 0.029 for 1018 reflections with I greater than or equal to 2 sigma. The molecule exists as a zwitterion in the crystal. The trans peptide backbone takes up a folded conformation at the middle glycylglycyl link accompanied by a significant nonplanarity up to delta omega of 8 degrees at the middle peptide and is relatively more extended at the two ends. The molecules are linked together intermolecularly in an infinite sequence of head to tail 1-4' hydrogen bonds, as is typical of charged peptides. It is interesting to note that while glycylglycylglycine takes up an extended beta-sheet conformation, addition of Leu to the N-terminal results in a bent conformation.
从乙醇 - 水溶液中生长出的L - 亮氨酰甘氨酰甘氨酰甘氨酸（LGGG，C12H22N4O5）晶体为正交晶系，空间群P2(1)2(1)2(1)，晶胞参数（在22 ± 3摄氏度时）为a = 9.337(1)，b = 10.995(1)，c = 15.235(1)埃，v = 1563.4埃³，Z = 4，实测密度Dobs = 1.29 g·cm⁻³，计算密度Dcalc = 1.279 g·cm⁻³。通过直接法解析晶体结构，并对1018个I大于或等于2σ的反射进行精修，R值为0.029。该分子在晶体中以两性离子形式存在。反式肽主链在中间甘氨酰甘氨酰连接部位呈折叠构象，中间肽段处的非平面性高达δω为8度，且两端相对更伸展。分子间通过典型的带电荷肽的头对尾1 - 4'氢键无限序列连接在一起。有趣的是，虽然甘氨酰甘氨酰甘氨酸呈伸展的β - 折叠构象，但在N端添加亮氨酸会导致构象弯曲。
