Reyes-Ruiz Jorge Mauricio, Chernyavsky Alex, Grando Sergei A, Glabe Charles
Department of Molecular Biology and Biochemistry, University of California Irvine, Irvine, California, USA.
Department of Dermatology, University of California Irvine, Irvine, California, USA.
J Biol Chem. 2025 Apr;301(4):108434. doi: 10.1016/j.jbc.2025.108434. Epub 2025 Mar 20.
Patients with pemphigus vulgaris (PV) develop IgG autoantibodies (AuAbs) binding to keratinocyte desmogleins (Dsg), acetylcholine (ACh) receptors, mitochondrial proteins, and some other self-antigens. In this study, we identified linear and discontinuous peptide tetrameric epitope segments (ES) of M3 muscarinic ACh receptor (M3AR) targeted by different anti-M3AR AuAbs. As positive controls, we identified Dsg1 and Dsg3 ES targeted by PV sera. Healthy individuals also possessed natural antibodies targeting M3AR, Dsg1 and Dsg3 epitopes that were different from those targeted by AuAbs produced by patients with PV. The two targeted M3AR pentameric ES encompass the 10 amino acids-long epitope LSEPTITFGT included the tetramer TFGT containing Thr235 which is a part of the ACh-binding pocket. Previously, it has been demonstrated that the anti-M3AR AuAb produces an agonist-like effect on downstream signaling, but its long-term effect is receptor desensitization. In this study, we compared the functional consequences of binding anti-M3AR AuAbs that target the ACh-binding pocket with that of AuAbs that target M3AR outside of its ACh-binding pocket. While the former AuAbs induced a very high elevation of phospholipase C, inositol triphosphate and diacylglycerol, which represents an agonist-like effect, the latter AuAbs produced a much weaker signaling response. These results indicate that patients with PV develop two types of anti-M3AR AuAbs. One type attaches to orthosteric, i.e., ACh-binding, site and elicits a strong signaling response comparable to that induced by a full pharmacologic agonist, whereas another type binds to an allosteric site and elicits submaximal signaling response comparable to that induced by a partial (allosteric) agonist.
寻常型天疱疮（PV）患者会产生与角质形成细胞桥粒芯糖蛋白（Dsg）、乙酰胆碱（ACh）受体、线粒体蛋白及其他一些自身抗原结合的IgG自身抗体（AuAbs）。在本研究中，我们鉴定了不同抗M3毒蕈碱型ACh受体（M3AR）AuAbs靶向的M3AR线性和不连续肽四聚体表位片段（ES）。作为阳性对照，我们鉴定了PV血清靶向的Dsg1和Dsg3 ES。健康个体也拥有靶向M3AR、Dsg1和Dsg3表位的天然抗体，这些表位与PV患者产生的AuAbs靶向的表位不同。两个靶向的M3AR五聚体ES包含10个氨基酸长的表位LSEPTITFGT，其中包括四聚体TFGT，其包含作为ACh结合口袋一部分的苏氨酸235。此前已证明，抗M3AR AuAb对下游信号传导产生激动剂样作用，但其长期作用是受体脱敏。在本研究中，我们比较了靶向ACh结合口袋的抗M3AR AuAbs与靶向M3AR ACh结合口袋之外区域的AuAbs结合的功能后果。虽然前者AuAbs诱导磷脂酶C、肌醇三磷酸和二酰基甘油非常高的升高，这代表激动剂样作用，但后者AuAbs产生的信号反应要弱得多。这些结果表明，PV患者产生两种类型的抗M3AR AuAbs。一种类型附着于正构位点，即ACh结合位点，并引发与完全药理激动剂诱导的信号反应相当的强烈信号反应，而另一种类型结合到变构位点，并引发与部分（变构）激动剂诱导的信号反应相当的次最大信号反应。
