THE STRUCTURE OF 2ZN PIG INSULIN CRYSTALS AT 1.5-A RESOLUTION
THE STRUCTURE OF 2ZN PIG INSULIN CRYSTALS AT 1.5-A RESOLUTION
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DOI：
10.1098/rstb.1988.0058
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发表时间：
1988-07-06
影响因子：
6.3
通讯作者：
VIJAYAN, NM
中科院分区：
文献类型：
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作者：
BAKER, EN;BLUNDELL, TL;VIJAYAN, NM
该论文描述了 2Zn 猪胰岛素菱面体晶体内原子的排列，如根据延伸至 1.5 ANG 的 X 射线数据计算的电子密度图所示。 (1.ANG. = 10-10 m = 10-1 nm) 在室温下并精炼至 R = 0.153。该晶胞含有2个锌离子、6个胰岛素分子和约3倍。 283个水分子。蛋白质分子中的原子看起来轮廓分明，不对称单元中的 102 个侧链中有 7 个已被指定为替代的无序位置。水分子上的电子密度已被解释为 349 个位点，其中 217 个权重为 1.0，126 个权重为 0.5，5 个为 0.33，1 个为 0.25，给出约。 282个分子。首先显示属于不对称单元的两条A链和B链的所有残基的位置和接触，然后显示它们在不同的两个胰岛素分子1和2中的排列的细节。随后，这些分子形成致密二聚体，并进一步聚集三个二聚体，形成围绕两个锌离子的六聚体。晶体中六聚体的堆积似乎存在相互矛盾的影响；相邻六聚体的组氨酸 B5 残基离子之间过于紧密的接触可能是二聚体两个分子之一的 A 链起始处的原子运动的原因，该运动启动了其他部分的运动，特别是在 B 链末端附近。在蛋白质结构构建的每个阶段，从残基到特定构象的链、分子、二聚体、六聚体和晶体，我们可以追踪相似基团堆积在一起、脂肪族基团在一起、芳香族基团在一起、氢键结构、正离子和负离子的堆积效果。在蛋白质分子之间，水分布在整个晶体中连续的空腔和通道中。超过一半的水分子直接与蛋白质原子形成氢键。它们通常与链和环中的其他水分子接触，这些水分子的无序度不断增加，这与它们在晶体中的运动相对应。在已建立的晶体结构中，我们接下来研究蛋白质分子内以及水与蛋白质、水与水之间的氢键分布；蛋白质中除八个活性原子外的所有原子都至少形成一个氢键。接下来我们讨论了不同接触对观察到的热参数的影响，以及将这些参数与单体、二聚体或六聚体作为一个整体的运动相关联的可能性。二聚体中分子 1 的相关性似乎最好。最后我们研究了整个晶体结构与胰岛素生物活性的关系。胰岛素受体的大尺寸使得当它结合形成受体复合物时，它很可能与胰岛素分子的表面进行大量接触。这些接触点中的一些，例如B24和B25苯丙氨酸，是由当这些残基被修饰时观察到的生物活性的变化所暗示的。晶体堆积产生的胰岛素链构象变化可以被视为胰岛素与受体接触可能引起的变化的模型，最终我们可能希望发现胰岛素受体复合物是否结晶。
The paper describes the arrangement of the atoms within rhombohedral crystals of 2Zn pig insulin as seen in electron density maps calculated from X-ray data extending to 1.5 .ANG. (1 .ANG. = 10-10 m = 10-1 nm) at room temperature and refined to R = 0.153. The unit cell contains 2 zinc ions, 6 insulin molecules and about 3 .times. 283 water molecules. The atoms in the protein molecules appear well defined, 7 of the 102 side chains in the asymmetric unit have been assigned alternative disordered positions. The electron density over the water molecules has been interpreted in terms of 349 sites, 217 weighted 1.0, 126 weighted 0.5, 5 at 0.33 and 1 at 0.25 giving ca. 282 molecules. The positions and contacts of all the residues belonging to the two A and B chains of the aysmmetric unit are shown first and then details of their arrangement in the two insulin molecules, 1 and 2, which are different. The formation from these molecules of a compact dimer and the further aggregation of three dimers to form a hexamer around two zinc ions, follows. It appears that in the packing of the hexamers in the crystal there are conflicting influences; too-close contacts between histidine B5 residues ion neighboring hexamers are probably responsible for movements of atoms at the beginning of the A chain of one of the two molecules of the dimer that initiate movements in other parts, particularly near the end of the B chain. At every stage of the building of the protein structure, residues to chains of definite conformation, molecules, dimers, hexamers and crystals, we can trace the effect of the packing of like groups to like, aliphatic groups together, aromatic groups together, hydrogen-bonded structures, positive and negative ions. Between the protein molecules, the water is distributed im cavities and channels that are continuous throughout the crystals. More than half the water molecules appear directly hydrogen bonded to protein atoms. These are generally in contact with other water molecules in chains and rings of increasing disorder, corresponding with their movement through the crystals. Within the established crystal structure we survey next the distribution of hydrogen bonds within the protein molecules and between water and protein and water and water; all but eight of the active atoms in the protein form at least one hydrogen bond. We follow with a discussion of the effect of different contacts on the observed thermal parameters and the possibility of correlating these with movements of the monomer, dimer or hexamer as a whole. The correlation seems best for molecule 1 in the dimer. Finally we examine the relation of the crystal structure as a whole to the biological activity of insulin. The large size of the insulin receptor makes it likely that when it combines to form the receptor complex, it makes a large number of contacts with the surface of the insulin molecule. Some of these points of contact, such as, for example, B24 and B25 phenylalanine, are suggested by the changes in biological activity observed when these residues are modified. The conformational changes in the insulin chains produced by crystal packing can be seen as a model for possible changes induced by insulin contacts with the receptor that eventually we may hope to discover if the insulin-receptor complex is crystallized.