Bodian D L, Jones E Y, Harlos K, Stuart D I, Davis S J
Laboratory of Molecular Biophysics, Oxford, UK.
Structure. 1994 Aug 15;2(8):755-66. doi: 10.1016/s0969-2126(94)00076-x.
The T-lymphocyte antigen CD2 is an adhesion molecule implicated in immune responses in vivo. The extracellular regions of the human and rat homologues of CD2 share only 45% sequence identity and bind different protein ligands. Comparison of the human and rat soluble CD2 (sCD2) structures should provide insights into the structural basis of cell surface recognition.
We therefore determined the crystal structure of a form of human sCD2 with single N-acetylglucosamine residues at each glycosylation site to 2.5 A resolution with an R-factor of 19.3%. It is composed of two immunoglobulin superfamily domains similar to those of rat sCD2, but the relative orientation of the domains in the two homologues differs by up to 20 degrees. An interaction involving the flat, highly charged, ligand binding GFCC'C" faces of crystallographically related human sCD2 molecules duplicates, in a different lattice, that observed in the rat sCD2 crystals.
Intramolecular flexibility appears to be a conserved feature of CD2. The head-to-head interaction between molecules represents a general model for interactions between adhesion molecules of this structural class. Ligand specificity may be influenced by the distribution of charged residues on the binding face.
T淋巴细胞抗原CD2是一种参与体内免疫反应的黏附分子。人源和大鼠同源CD2的细胞外区域序列同一性仅为45%，且结合不同的蛋白质配体。比较人源和大鼠可溶性CD2（sCD2）的结构应能深入了解细胞表面识别的结构基础。
因此，我们确定了一种在每个糖基化位点带有单个N-乙酰葡糖胺残基的人源sCD2形式的晶体结构，分辨率达到2.5 Å，R因子为19.3%。它由两个与大鼠sCD2相似的免疫球蛋白超家族结构域组成，但这两个同源物中结构域的相对取向相差高达20度。在晶体学相关的人源sCD2分子中，涉及平坦、高电荷、配体结合的GFCC'C"面的相互作用在不同晶格中重复了在大鼠sCD2晶体中观察到的情况。
分子内灵活性似乎是CD2的一个保守特征。分子间的头对头相互作用代表了这类结构的黏附分子之间相互作用的一般模型。配体特异性可能受结合面上带电残基分布的影响。
