ON THE ATTRIBUTION OF BINDING-ENERGY IN ANTIGEN-ANTIBODY COMPLEXES MCPC-603, D1.3, AND HYHEL-5
ON THE ATTRIBUTION OF BINDING-ENERGY IN ANTIGEN-ANTIBODY COMPLEXES MCPC-603, D1.3, AND HYHEL-5
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DOI：
10.1021/bi00437a034
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发表时间：
1989-05-30
期刊：
影响因子：
2.9
通讯作者：
SAUL, FA
中科院分区：
文献类型：
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作者：
NOVOTNY, J;BRUCCOLERI, RE;SAUL, FA
使用抗原抗体复合物 McPC 603、D1.3 和 HyHEL-5 的 X 射线坐标，我们对伴随着 McPC 603 Fv 片段与磷酸胆碱以及 D1.3 或 HyHEL-5 Fv 片段与鸡蛋清溶菌酶的非共价复合物形成的吉布斯自由能变化 (.DELTA.G) 进行了半定量估计。我们的经验 .DELTA.G 函数隐式地包含了溶剂效应，具有以下组成部分：疏水力、溶剂修饰静电、侧链构象熵的变化、平移/总体旋转熵变化以及稀释（克拉蒂）熵项。计算出的ΔG范围与实验测定的McPC 603和D1.3复合物的ΔG相匹配，并且在HyHEL-5的情况下高估了它（即，给出了更大的负值）。针对HyHEL-5复合物计算的所选抗体残基的相对ΔG贡献与在定点诱变实验中独立确定的那些一致。对所有三个复合物中的ΔG属性的分析表明，只有少数氨基酸可能对结合能量有积极贡献。这些形成了总抗原-抗体接触表面的一个子集。在抗体中，抗原结合腔的底部决定了结合的能量，而在溶菌酶中，能量上最重要的残基定义了小的（2.5-3 nm2）“能量”表位。因此，出现了蛋白质抗原性的概念，涉及由能量抗原表位介导的主动、有吸引力的贡献和由周围接触区域贡献的被动表面互补性。溶菌酶的D1.3能量表位涉及Gly 22、Gly 117和Gln 121； HyHEL-5表位由Arg 45和Arg 68组成。这些也是通过实验确定的必需抗原残基。上述位置属于溶菌酶表面最突出的部分，其主链并不是特别柔韧。六个不同抗体结合区域的最小二乘分析表明，VH-VL界面β-桶的几何形状非常保守，没有表明复合物形成时结构域-结构域接触的显着变化。
Using X-ray coordinates of antigen-antibody complexes McPC 603, D1.3, and HyHEL-5, we made semiquantitative estimates of Gibbs free energy changes (.DELTA.G) accompanying noncovalent complex formation of the McPC 603 Fv fragment with phosphocholine and the D1.3 or HyHEL-5 Fv fragments with hen egg white lysozyme. Our empirical .DELTA.G function, which implicitly incorporates solvent effects, has the following components: hydrophobic force, solvent-modified electrostatics, changes in side-chain conformational entropy, translational/overall rotational entropy changes, and the dilutional (cratic) entropy term. The calculated .DELTA.G ranges matched the experimentally determined .DELTA.G of McPC 603 and D1.3 complexes and overestimated it (i.e., gave a more negative value) in the case of HyHEL-5. Relative .DELTA.G contributions of selected antibody residues, calculated for HyHEL-5 complexes, agreed with those determined independently in site-directed mutagenesis experiments. Analysis of .DELTA.G attribution in all three complexes indicated that only a small number of amino acids probably contribute actively to binding energetics. These form a subset of the total antigen-antibody contact surface. In the antibodies, the bottom part of the antigen binding cavity dominated the energetics of binding whereas in lysozyme, the energetically most important residues defined small (2.5-3 nm2) "energetic" epitopes. Thus, a concept of protein antigenicity emerges that involves the active, attractive contributions mediated by the energetic antigenic epitopes and the passive surface complementarity contributed by the surrounding contact area. The D1.3 energetic epitope of lysozyme involved Gly 22, Gly 117, and Gln 121; the HyHEL-5 epitope consisted of Arg 45 and Arg 68. These are also the essential antigenic residues determined experimentally. The above positions belong to the most protruding parts of the lysozyme surface, and their backbones are not exceptionally flexible. Least-squares analysis of six different antibody binding regions indicated that the geometry of the VH-VL interface .beta.-barrel is well conserved, giving no indication of significant changes in domain-domain contacts upon complex formation.