Gadkari Rupali A, Sandhya S, Sowdhamini R, Dighe Rajan R
Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560012, India.
Mol Cell Endocrinol. 2007 Jan 2;260-262:23-32. doi: 10.1016/j.mce.2006.07.006. Epub 2006 Oct 11.
The common feature of receptors and antibodies against the ligand is that both display very specific, high affinity binding towards the ligand. Therefore, it can be hypothesized that the paratope of antibodies may exhibit homology with distinct domains of the receptor. By locating the hormone epitopes and determining the structure of the paratopes, it should be possible to identify the contact points between the ligand and the receptor. This hypothesis has been tested using hCG monoclonal antibodies (MAbs) recognizing different epitopes and having different effects on hormone binding and response. The beta subunit and heterodimer specific antibodies inhibited both hormone binding and response, while the alpha subunit specific antibodies inhibited response without affecting binding. The single chain fragment variables (ScFvs) produced from these antibodies also retained the properties of the parent antibodies. The amino acid sequences of the ScFvs exhibited homology to different regions of the receptor; the beta subunit specific antibody being homologous to the concave surface of the leucine rich repeats (LRR) of the receptor, particularly the concave surface of the LRRs, while the heterodimer specific antibody showed homology to the hinge region. The alpha subunit specific antibody showed homology to the transmembrane domain of the receptor. The exact locations of the epitopes of the monoclonal antibodies in the hormone molecule have also been identified. The data presented here also support the model of glycoprotein hormone-receptor interaction in which the hormone binds to the extracellular domain through the beta subunit and then the alpha subunit is brought in contact with the transmembrane domain leading to signal transduction.
受体和针对配体的抗体的共同特征是，两者都对配体表现出非常特异、高亲和力的结合。因此，可以推测抗体的互补决定区可能与受体的不同结构域具有同源性。通过定位激素表位并确定互补决定区的结构，应该有可能识别配体与受体之间的接触点。这一假设已通过使用识别不同表位且对激素结合和反应具有不同影响的人绒毛膜促性腺激素单克隆抗体（MAb）进行了验证。β亚基特异性抗体和异二聚体特异性抗体均抑制激素结合和反应，而α亚基特异性抗体抑制反应但不影响结合。由这些抗体产生的单链可变片段（ScFv）也保留了亲本抗体的特性。ScFv的氨基酸序列与受体的不同区域具有同源性；β亚基特异性抗体与受体富含亮氨酸重复序列（LRR）的凹面同源，特别是LRR的凹面，而异二聚体特异性抗体与铰链区同源。α亚基特异性抗体与受体的跨膜结构域同源。还确定了单克隆抗体表位在激素分子中的精确位置。本文提供的数据也支持糖蛋白激素-受体相互作用模型，即激素通过β亚基与细胞外结构域结合，然后α亚基与跨膜结构域接触导致信号转导。
