Eddins Donnie, Sproul Adrian D, Lyford Lisa K, McLaughlin James T, Rosenberg Robert L
Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Am J Physiol Cell Physiol. 2002 Nov;283(5):C1454-60. doi: 10.1152/ajpcell.00204.2002.
Neuronal alpha7 nicotinic ACh receptors (nAChRs) are permeable to and modulated by Ca2+, Ba2+, and Sr2+. These permeant divalent cations interact with slowly desensitizing L247T alpha7 nAChRs to increase the potency and maximal efficacy of ACh, increase the efficacy of dihydro-beta-erythroidine (DHbetaE), and increase agonist-independent activity. Mutation of glutamate 172 (E172) to glutamine or cysteine eliminated these effects of permeant divalent cations. 2-(Trimethylammonium)ethyl methanethiosulfonate (MTSET), a cysteine-modifying reagent directed at water-accessible thiols, inhibited ACh-evoked currents of E172C/L247T alpha7 nAChRs by >90%, demonstrating that E172 was accessible to permeant ions. The data are consistent with a model of alpha7 receptors, derived from the crystal structure of the ACh binding protein (AChBP) from Lymnaea stagnalis, in which E172 projects toward the lumen of the extracellular vestibule. The observations that E172 was essential for divalent cation modulation of L247T alpha7 nAChRs and was accessible to permeating ions suggest that this residue participates in coupling ion permeation with modulation of receptor activity.
神经元α7烟碱型乙酰胆碱受体（nAChRs）可通透Ca2+、Ba2+和Sr2+并受其调节。这些可通透的二价阳离子与缓慢脱敏的L247Tα7 nAChRs相互作用，以提高乙酰胆碱的效力和最大效能，提高二氢β-刺桐啶（DHbetaE）的效能，并增加非激动剂依赖性活性。将谷氨酸172（E172）突变为谷氨酰胺或半胱氨酸可消除这些可通透二价阳离子的作用。2-（三甲铵）乙基甲硫代磺酸盐（MTSET）是一种针对可接触水的硫醇的半胱氨酸修饰试剂，可抑制E172C/L247Tα7 nAChRs的乙酰胆碱诱发电流达90%以上，表明E172可被可通透离子接触。这些数据与源自椎实螺乙酰胆碱结合蛋白（AChBP）晶体结构的α7受体模型一致，其中E172朝向细胞外前庭腔投射。E172对L247Tα7 nAChRs的二价阳离子调节至关重要且可被渗透离子接触这一观察结果表明，该残基参与将离子通透与受体活性调节相偶联。
