Garrett T P, Wang J, Yan Y, Liu J, Harrison S C
Howard Hughes Medical Institute, Cambridge, MA.
J Mol Biol. 1993 Dec 5;234(3):763-78. doi: 10.1006/jmbi.1993.1625.
The structure of a fragment of human CD4 containing two immunoglobulin (Ig)-like domains has been determined by X-ray crystallography and refined at 2.2 A resolution. The structure determination involved iterative building and simulated-annealing refinement, beginning with a partial model. Comparison of domain 1 with an Ig variable domain shows that CD4 has a long and prominent CDR2-like loop (the C"C" corner) and shortened CC' and FG loops (which mediate dimerization in IgV modules). Comparison of domain 2 with Ig modules and domain 1 shows that it can be described as a truncated Ig V domain, in which strands C" and D are deleted. The intersheet disulfide in domain 2 is absent, and there is an altered packing of the two beta-sheets together with a remodeling of the hydrophobic core. The interface between domains 1 and 2 is a lap joint with an extensive hydrophobic surface. The key features of domain 1 that contribute to the interface are found at corresponding positions in domain 2, leading us to propose that the contact between domains 2 and 3 will resemble the one between domains 1 and 2.
通过X射线晶体学确定了包含两个免疫球蛋白（Ig）样结构域的人CD4片段的结构，并在2.2埃分辨率下进行了精修。结构测定从一个部分模型开始，涉及迭代构建和模拟退火精修。将结构域1与Ig可变结构域进行比较表明，CD4具有一个长而突出的类似CDR2的环（C“-C”角）以及缩短的C-C'和F-G环（它们在IgV模块中介导二聚化）。将结构域2与Ig模块和结构域1进行比较表明，它可被描述为一个截短的Ig V结构域，其中C“和D链被删除。结构域2中片层间二硫键不存在，并且两个β-片层的堆积发生改变，同时疏水核心也进行了重塑。结构域1和2之间的界面是一个具有广泛疏水表面的搭接接头。在结构域2的相应位置发现了对该界面有贡献的结构域1的关键特征，这使我们提出结构域2和3之间的接触将类似于结构域1和2之间的接触。
