Kuner T, Wollmuth L P, Karlin A, Seeburg P H, Sakmann B
Zentrum für Molekulare Biologie, der Universität Heidelberg (ZMBH), Federal Republic of Germany.
Neuron. 1996 Aug;17(2):343-52. doi: 10.1016/s0896-6273(00)80165-8.
The structure of the NMDA receptor channel M2 segment was investigated by probing the extracellular and cytoplasmic faces of cysteine-substituted NR1-NR2C channels with charged sulfhydryl-specific reagents. The pattern of accessible positions suggests that the M2 segment forms a channel-lining loop originating and ending on the cytoplasmic side of the channel, with the ascending limb in an alpha-helical structure and the descending limb in an extended structure. A functionally critical asparagine (N-site) is positioned at the tip of the loop, and a cluster of hydrophilic residues of the descending limb, adjacent to the tip, forms the narrow constriction of the channel. An apparent asymmetric positioning of the NR1- and NR2-subunit N-site asparagines may account for their unequal role in Ca2+ permeability and Mg2+ block.
通过使用带电荷的巯基特异性试剂探测半胱氨酸取代的NR1-NR2C通道的细胞外和细胞质面，研究了NMDA受体通道M2片段的结构。可及位置的模式表明，M2片段形成一个通道内衬环，起始和终止于通道的细胞质侧，上升支呈α螺旋结构，下降支呈伸展结构。一个功能关键的天冬酰胺（N位点）位于环的顶端，下降支与顶端相邻的一簇亲水残基形成通道的狭窄收缩处。NR1和NR2亚基N位点天冬酰胺明显的不对称定位可能解释了它们在Ca2+通透性和Mg2+阻断中作用的不平等。
