Ohno S, Mori N, Matsunaga T
Proc Natl Acad Sci U S A. 1985 May;82(9):2945-9. doi: 10.1073/pnas.82.9.2945.
Although the antigen-binding pocket of all antibodies consists of VL + VH dimers (where VL and VH represent immunoglobulin light and heavy chain regions, respectively), subgroups of their VH largely determine their antigen-binding specificities. This VH subgroup dependence automatically relegates subsidiary roles to VL as a whole and to the complementarity-determining region 3 (CDR-3) of VH encoded by independent diversity (D) and joining (J) coding segments in determining antigen-binding specificities of individual antibodies. As a sequel to our previous paper, which emphasized the role conserved residues in CDR-1 and CDR-2 of VH play in general shaping of the primordial antigen-binding cavity, here we propose that the three short clusters of amino acid sequences in CDR-1 and CDR-2 that are placed in the immediate vicinity of the tryptophan loop primarily determine subgroup-dependent antigen preference of individual VH, therefore, antibodies. The three clusters are the 31st to 35th positions of CDR-1 and the 50th to 52nd and 58th to 60th positions of CDR-2. Of those, the 32nd, 34th, 51st, and 59th positions tend to be occupied by tyrosine, methionine, isoleucine, and tyrosine, respectively. Nevertheless, free amino acid substitutions at the remaining seven sites can generate 20(7) or 1.28 X 10(9) varieties of amino acid sequence combinations. Some of these astronomically numerous sequence combinations no doubt contribute to the maintenance of the vast repertoire of antigen-combining diversity, which might be as large as 10(7), whereas others serve to vary binding affinities toward the same antigen. Ironically, but not surprisingly, a single nonconservative amino acid substitution at one of these sites often suffices to change the antigen preference of VH from one to another, whereas more substitutions affecting two or more clusters are apparently required to change the binding affinity toward the same antigen. In the case of mouse anti-p-azophenylarsonate antibodies, the principle of VH subgroup dependence is violated, their VH belonging to either subgroup 1 or 3. It appears that the mouse genome lacks anti-p-azophenylarsonate germ line VH, residues of CDR-3 derived from one particular JH coding segment coming to rescue to cope with this unnatural man-made antigen.
尽管所有抗体的抗原结合口袋均由VL + VH二聚体组成（其中VL和VH分别代表免疫球蛋白轻链和重链区域），但其VH亚组在很大程度上决定了它们的抗原结合特异性。这种对VH亚组的依赖性自动将VL整体以及由独立多样性（D）和连接（J）编码片段编码的VH互补决定区3（CDR-3）在决定单个抗体的抗原结合特异性方面降为次要作用。作为我们之前强调VH的CDR-1和CDR-2中保守残基在原始抗原结合腔的总体形成中所起作用的论文的续篇，在此我们提出，位于色氨酸环紧邻位置的CDR-1和CDR-2中的三个短氨基酸序列簇主要决定了单个VH进而抗体的亚组依赖性抗原偏好。这三个簇分别是CDR-1的第31至35位以及CDR-2的第50至52位和第58至60位。其中，第32、34、51和59位往往分别被酪氨酸、甲硫氨酸、异亮氨酸和酪氨酸占据。然而，其余七个位点的自由氨基酸替换可产生20(7) 即1.28×10(9)种氨基酸序列组合。这些数量极其庞大的序列组合中，有些无疑有助于维持可能多达10(7)的巨大抗原结合多样性库，而其他一些则用于改变对同一抗原的结合亲和力。具有讽刺意味但并不奇怪的是，这些位点中的一个发生单个非保守氨基酸替换通常就足以将VH的抗原偏好从一种改变为另一种，而显然需要更多影响两个或更多簇的替换才能改变对同一抗原的结合亲和力。在小鼠抗对氨基苯胂酸抗体的情况下，违反了VH亚组依赖性原则，其VH属于亚组1或3。看来小鼠基因组缺乏抗对氨基苯胂酸种系VH，来自一个特定JH编码片段的CDR-3残基前来救援以应对这种非天然的人工合成抗原。
