Hardman K D, Wood M K, Schiffer M, Edmundson A B, Ainsworth C F
Proc Natl Acad Sci U S A. 1971 Jul;68(7):1393-7. doi: 10.1073/pnas.68.7.1393.
An electron density map produced by x-ray diffraction analysis of concanavalin A has been calculated to 4.25 A from data of three isomorphous heavy atom derivatives. The crystals are orthorhombic, with unit-cell dimensions of 63.1, 87.0, and 89.2 A for a, b, and c, respectively. The space group is I222, with eight asymmetric units per unit cell. The crystal asymmetric unit contains 27,000 daltons of protein and reflects the chemically unique component (protomer) within the oligomer. Separate chemical studies indicate that the protomer consists of two different polypeptide chains. Four protomers cluster around the intersection of three mutually perpendicular two-fold rotation axes to form a molecule of 108,000 daltons. The molecule can also be subdivided into two-protomer units of 54,000 daltons. Within the two-protomer unit, there are significantly more contacts joining the protomers than there are between adjacent two-protomer units that form the total molecule. These results provide a possible explanation for disagreement in molecular weights obtained in previous ultracentrifugal studies.
通过对伴刀豆球蛋白A的X射线衍射分析产生的电子密度图，已根据三种同晶型重原子衍生物的数据计算至4.25埃。晶体为正交晶系，a、b、c方向的晶胞尺寸分别为63.1、87.0和89.2埃。空间群为I222，每个晶胞有八个不对称单元。晶体不对称单元包含27,000道尔顿的蛋白质，反映了寡聚体中化学上独特的组分（原体）。单独的化学研究表明，原体由两条不同的多肽链组成。四个原体围绕三个相互垂直的二次旋转轴的交点聚集，形成一个108,000道尔顿的分子。该分子也可细分为54,000道尔顿的双原体单元。在双原体单元内，连接原体的接触点明显多于形成整个分子的相邻双原体单元之间的接触点。这些结果为先前超速离心研究中获得的分子量不一致提供了一种可能的解释。
