Bruderer U, Peyton D H, Barbar E, Fellman J H, Rittenberg M B
Department of Microbiology and Immunology, Oregon Health Sciences University, Portland 97201.
Biochemistry. 1992 Jan 21;31(2):584-9. doi: 10.1021/bi00117a040.
We have shown previously that anti-phenylphosphocholine antibodies elicited by phosphocholine-keyhole limpet hemocyanin can be divided into two populations according to their ability to recognize the two hapten analogues p-nitrophenylphosphocholine (NPPC) and p-nitrophenyl 3,3-dimethylbutyl phosphate (NPDBP). These analogues differ from each other in that NPPC has a positively charged nitrogen in the choline moiety, whereas NPDBP lacks the positively charged nitrogen. Group II-A antibodies bind only NPPC, whereas group II-B antibodies bind both ligands. Here, by infrared and nuclear magnetic resonance spectroscopic investigations, we find that when free in solution NPPC has a predominantly fixed structure in which the termini approach each other, probably due to electrostatic interactions within the molecule; this "bent" structural feature is retained when the ligand is bound by antibody. In contrast, the structure of unbound NPDBP is less fixed, being characterized by rapidly interchanging conformations corresponding to an open chain structure with less overall proximity of the termini compared to NPPC. The overall shape of NPPC is essentially unaltered by binding, whereas in the case of NPDBP what was a minor conformation in the unbound state becomes the predominate conformation of the bound ligand. Thus, our results are consistent with these antibodies providing a molecular template for stabilizing the conformation of the bound ligand.
我们之前已经表明，由磷酸胆碱-钥孔血蓝蛋白引发的抗苯基磷酸胆碱抗体，根据其识别两种半抗原类似物对硝基苯基磷酸胆碱（NPPC）和对硝基苯基3,3-二甲基丁基磷酸酯（NPDBP）的能力，可分为两个群体。这些类似物的不同之处在于，NPPC在胆碱部分有一个带正电荷的氮，而NPDBP缺乏带正电荷的氮。II-A组抗体只结合NPPC，而II-B组抗体结合两种配体。在这里，通过红外和核磁共振光谱研究，我们发现当NPPC在溶液中游离时，它主要具有一种固定结构，其中末端相互靠近，这可能是由于分子内的静电相互作用；当配体与抗体结合时，这种“弯曲”的结构特征得以保留。相比之下，未结合的NPDBP的结构不太固定，其特征是构象快速互换，对应于一种开放链结构，与NPPC相比，末端之间的总体接近度较低。NPPC的整体形状在结合后基本不变，而在NPDBP的情况下，未结合状态下的次要构象变成了结合配体的主要构象。因此，我们的结果与这些抗体为稳定结合配体的构象提供分子模板的观点一致。
