DETAILED ANALYSIS OF THE FREE AND BOUND CONFORMATIONS OF AN ANTIBODY - X-RAY STRUCTURES OF FAB 17/9 AND 3 DIFFERENT FAB-PEPTIDE COMPLEXES
DETAILED ANALYSIS OF THE FREE AND BOUND CONFORMATIONS OF AN ANTIBODY - X-RAY STRUCTURES OF FAB 17/9 AND 3 DIFFERENT FAB-PEPTIDE COMPLEXES
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DOI：
10.1006/jmbi.1993.1663
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发表时间：
1993-12-20
影响因子：
5.6
通讯作者：
WILSON, IA
中科院分区：
文献类型：
--
作者：
SCHULZEGAHMEN, U;RINI, JM;WILSON, IA
已确定 Fab 17/9 的新斜方晶型与流感病毒血凝素的 7 聚体肽（HA1 101-107，乙酰化和酰胺化）形成复合物。三维结构分辨率为 2·8 Å，与之前确定的两种 Fab 17/9-肽 (HA1 100-108) 复合物相比，具有改进的精化和更好的几何形状，有助于详细描述 Fab-肽相互作用。 Fab 17/9 的所有三种肽复合物中的结合袋和肽抗原结构相似。该肽采用延伸构象（残基 100 至 103）和 I 型反转（残基 104 至 107）。此外，此处描述的抗原决定簇与之前的表位作图研究密切相关。游离和抗原结合的 Fab 的结构说明了诱导契合作为抗体-抗原识别机制的作用。在肽结合后，Fab 17/9 经历较大的构象变化，主要是在 H3 环中。结果，配体 Fab 中结合袋的形状发生显着变化。然而，其他高变环（L2、L3、H1 和 H2）的主链构象在自由结构和结合结构之间没有显着差异。 L1环的构象在所有结构中也得到维持，但其相对于框架的位置在不同的晶体环境中有所不同。 Fab-肽复合物在三个不同空间群中的三种 X 射线结构的可用性使得可以清楚地区分晶体堆积和抗原结合作为结构差异的原因。观察到两种不同的 H3 环构象，游离的和结合的，没有其他证据表明高变环 (CDR) 的多种构象或游离或结合形式的灵活性增加。
A new orthorhombic crystal form of Fab 17/9 has been determined in complex with a 7-mer peptide from influenza virus hemagglutinin (HA1 101-107, acetylated and amidated). The three-dimensional structure was resolved to 2·8 Å, with an improved refinement and better geometry than two previously determined Fab 17/9-peptide (HA1 100-108) complexes, facilitating a detailed description of the Fab-peptide interactions. The binding pockets and the peptide antigen are structurally similar in all three peptide complexes of Fab 17/9. The peptide adopts an extended conformation (residues 100 to 103) and a type I reverse turn (residues 104 to 107). Additionally, the antigenic determinant described here correlates well with previous epitope mapping studies.The structures of the free and antigen bound Fab illustrate the role of induced fit as a mechanism for antibody-antigen recognition. Fab 17/9 undergoes a large conformational change, mainly in the H3 loop, upon peptide binding. As a result, the shape of the binding pocket changes substantially in the liganded Fab. However, the backbone conformations of the other hypervariable loops (L2, L3, H1 and H2) show no significant difference between free and bound structures. The conformation of the L1 loop is also maintained in all structures, but its position relative to the framework varies in different crystal environments. The availability of three X-ray structures of an Fab-peptide complex in three different space groups makes it possible to clearly distinguish between crystal packing and antigen binding as the cause of structural differences. Two distinct H3-loop conformations, free and bound, are observed with no evidence otherwise for multiple conformations of the hypervariable loops (CDRs) or increased flexibility in either the free or bound forms.