CRYSTAL-STRUCTURES OF AN ANTIBODY TO A PEPTIDE AND ITS COMPLEX WITH PEPTIDE ANTIGEN AT 2.8 A
CRYSTAL-STRUCTURES OF AN ANTIBODY TO A PEPTIDE AND ITS COMPLEX WITH PEPTIDE ANTIGEN AT 2.8 A
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DOI：
10.1126/science.2333521
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发表时间：
1990-05-11
期刊：
影响因子：
56.9
通讯作者：
WILSON, IA
中科院分区：
文献类型：
--
作者：
STANFIELD, RL;FIESER, TM;WILSON, IA
在2.8埃下测定了肽的抗体及其与肽抗原的复合物的三维结构。分辨率该抗原是肌红蛋白（Mhr）C螺旋的合成19-氨基酸肽同源物。未配体的Fab“晶体是正交的，每个不对称单元具有两个分子，而复合物晶体是六边形的，每个不对称单元具有一个分子。Fab“和Fab”-肽复合物结构已经通过分子置换方法独立地解析，并且分别具有0.197和0.215的晶体学R因子，其中不包括水分子。肽序列的氨基末端部分（NH 2-Glu-Val-Val-Pro-His-Lys-Lys）在Fab“-肽复合物的电子密度图中可清楚地解释，并采用了明确定义的II β-型。在凹的抗原结合口袋中转动。天然Mhr中的相同肽氨基酸序列是α-螺旋状的当与Fab“结合时，肽构象与Fab”与天然Mhr的结合不一致，并且表明结合只能发生于天然Mhr的构象改变形式或apo-Mhr。免疫作图先前将该序列鉴定为肽表位，并且其良好的特异性与结构分析良好相关。结合口袋包括大百分比的疏水残基。肽和抗体的埋入表面形状互补，分别覆盖460埃2和540埃2。这两种结构现在能够比较游离状态和抗原复合状态的特异性单克隆Fab“。虽然当肽结合时未观察到抗体的重大变化，但存在一些小但显著的侧链和主链重排。
The three-dimensional structures of an antibody to a peptide and its complex with the peptide antigen have been determined at 2.8 .ANG. resolution. The antigen is a synthetic 19-amino acid peptide homology of the C helix of myohemerythrin (Mhr). The unliganded Fab'' crystals are orthorhombic with two molecules per asymmetric unit, whereas the complex crystals are hexagonal with one molecule per asymmetric unit. The Fab'' and the Fab''-peptide complex structures have been solved independently by molecular replacement methods and have crystallographic R factors of 0.197 and 0.215, respectively, with no water molecules included. The amino-terminal portion of the peptide sequence (NH2-Glu-Val-Val-Pro-His-Lys-Lys) is clearly interpretable in the electron density map of the Fab''-peptide complex and adopts a well-defined type II .beta.-turn in the concave antigen binding pocket. This same peptide amino acid sequence in native Mhr is .alpha.-helical. The peptide conformation when bound to the Fab'' is inconsistent with binding of the Fab'' to native Mhr, and suggests that binding can only occur to conformationally altered forms of the native Mhr or to apo-Mhr. Immunological mapping previously identified this sequence as the peptide epitope, and its fine specificity correlates well with the structural analysis. The binding pocket includes a large percentage of hydrophobic residues. The buried surfaces of the peptide and the antibody are complementary in shape and cover 460 .ANG.2 and 540 .ANG.2, respectively. These two structures now enable a comparison of a specific monoclonal Fab'' both in its free and antigen complexed state. While no major changes in the antibody were observed when peptide was bound, there were some small but significant side chain and main chain rearrangements.