Tulip W R, Varghese J N, Webster R G, Laver W G, Colman P M
CSIRO Division of Biomolecular Engineering, Parkville, Victoria, Australia.
J Mol Biol. 1992 Sep 5;227(1):149-59. doi: 10.1016/0022-2836(92)90688-g.
The site on influenza virus N9 neuraminidase recognized by NC41 monoclonal antibody comprises 19 amino acid residues that are in direct contact with 17 residues on the antibody. Single sequence changes in some of the neuraminidase residues in the site markedly reduce antibody binding. However, two mutants have been found within the site, Ile368 to Arg and Asn329 to Asp selected by antibodies other than NC41, and these mutants bind NC41 antibody with only slightly reduced affinity. The three-dimensional structures of the two mutant N9-NC41 antibody complexes as derived from the wild-type complex are presented. Both structures show that some amino acid substitutions can be accommodated within an antigen-antibody interface by local structural rearrangements around the mutation site. In the Ile368 to Arg mutant complex, the side-chain of Arg368 is shifted by 2.9 A from its position in the uncomplexed mutant and a shift of 1.3 A in the position of the light chain residue HisL55 with respect to the wild-type complex is also observed. In the other mutant, the side-chain of Asp329 appears rotated by 150 degrees around C alpha-C beta with respect to the uncomplexed mutant, so that the carboxylate group is moved to the periphery of the antigen-antibody interface. The results provide a basis for understanding some of the potential structural effects of somatic hypermutation on antigen-antibody binding in those cases where the mutation in the antibody occurs at antigen-contacting residues, and demonstrate again the importance of structural context in evaluating the effect of amino acid substitutions on protein structure and function.
流感病毒N9神经氨酸酶上被NC41单克隆抗体识别的位点包含19个氨基酸残基，这些残基与抗体上的17个残基直接接触。该位点中一些神经氨酸酶残基的单序列变化会显著降低抗体结合。然而，在该位点内发现了两个突变体，即由NC41以外的抗体选择的Ile368突变为Arg以及Asn329突变为Asp，这些突变体与NC41抗体结合时亲和力仅略有降低。本文展示了由野生型复合物衍生而来的两种突变N9 - NC41抗体复合物的三维结构。两种结构均表明，一些氨基酸取代可通过突变位点周围的局部结构重排在抗原 - 抗体界面内得到容纳。在Ile368突变为Arg的突变体复合物中，Arg368的侧链相对于未结合的突变体移动了2.9 Å，并且相对于野生型复合物，轻链残基HisL55的位置也有1.3 Å的移动。在另一个突变体中，Asp329的侧链相对于未结合的突变体围绕Cα - Cβ旋转了150度，使得羧基基团移至抗原 - 抗体界面的外围。这些结果为理解在抗体中抗原接触残基发生突变的情况下，体细胞超突变对抗原 - 抗体结合的一些潜在结构影响提供了基础，并再次证明了结构背景在评估氨基酸取代对蛋白质结构和功能影响方面的重要性。
