Desensitization of the nicotinic acetylcholine receptor mainly involves a structural change in solvent-accessible regions of the polypeptide backbone
Desensitization of the nicotinic acetylcholine receptor mainly involves a structural change in solvent-accessible regions of the polypeptide backbone
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DOI：
10.1021/bi962845m
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发表时间：
1997-03-25
期刊：
影响因子：
2.9
通讯作者：
Chew, JP
中科院分区：
文献类型：
--
作者：
Baenziger, JE;Chew, JP
烟碱型乙酰胆碱受体（nAChR）的红外光谱之间的差异记录使用衰减全反射技术在存在和不存在的氨甲酰胆碱表现出复杂的模式的积极和消极的频带，提供了一个光谱图的结构变化时，发生在nAChR激动剂结合和随后的脱敏。在（H2O）-H-1缓冲液中记录的差谱的酰胺I区域中，在1655 cm（-1）和1620 cm（-1）附近观察到两个相对较强的条带，这两个条带先前被解释为β-折叠向α-螺旋的净转化或伴随β-折叠和/或转角结构变化的跨膜α-螺旋的重新取向[Baenziger，J.E.，米勒，K. W.，& Rothschild，K. J.（1993）Biochemistry 32，5448-5454]。然而，在（H2O）-H-2缓冲液中记录的差异光谱揭示，在肽H-1/H-2交换时酰胺I区域中的这些和其它差异带经历频率的下移，其比通常对于α-螺旋或β-折叠的酰胺I振动观察到的频率的下移大得多。在将nAChR预先暴露于（H2O）-H-2的数分钟或数小时内，在（H2O）-H-2缓冲液中记录的差异光谱显示出与在将nAChR预先暴露于（H2O）-H-2的3天后记录的差异光谱中观察到的相同的酰胺I差异带位移。大多数参与配体结合和静止到脱敏构象变化的肽，以及在差谱中产生谱带的肽，因此在秒到分钟的时间尺度上将它们的氢交换为氘。差谱带的频率，差谱带的幅度在肽H-1/H-2交换时发生位移，以及在差谱中产生酰胺I谱带的那些结构的氢氘交换动力学的快速性都表明，通道失活的脱敏状态的形成主要是由溶剂中的构象变化引起的。与离子通道门附近的大的结构扰动相反，多肽骨架的可接近的膜外区域。激动剂结合位点的构象变化可能是脱敏后通道失活的主要原因。
The difference between infrared spectra of the nicotinic acetylcholine receptor (nAChR) recorded using the attenuated total reflectance technique in the presence and absence of carbamylcholine exhibits a complex pattern of positive and negative bands that provides a spectral map of the structural changes that occur in the nAChR upon agonist binding and subsequent desensitization. Two relatively intense bands are observed in the amide I region of the difference spectra recorded in (H2O)-H-1 buffer near 1655 cm(-1) and 1620 cm(-1) that were previously interpreted in terms of either a net conversion of beta-sheet to alpha-helix or a reorientation of transmembrane alpha-helix accompanied by a change in structure of beta-sheet and/or turn [Baenziger, J. E., Miller, K. W., & Rothschild, K. J. (1993) Biochemistry 32, 5448-5454], However, difference spectra recorded in (H2O)-H-2 buffer reveal that these and other difference bands in the amide I region undergo downshifts in frequency upon peptide H-1/H-2 exchange that are much larger than the downshifts in frequency that are typically observed for the amide I vibrations of either alpha-helix or beta-sheet. Difference spectra recorded in (H2O)-H-2 buffer within either minutes or hours of prior exposure of the nAChR to (H2O)-H-2 exhibit the same amide I difference band shifts that are observed in difference spectra recorded after 3 days prior exposure of the nAChR to (H2O)-H-2. Most Of the peptides that are involved in both ligand binding and the resting to desensitized conformational change and that give rise to bands in the difference spectra therefore exchange their hydrogens for deuterium on the seconds to minutes time scale, The frequencies of the difference bands, the magnitudes of the difference band shifts upon peptide H-1/H-2 exchange, and the rapidity of the hydrogen deuterium exchange kinetics of those structures that give rise to amide I bands in the difference spectra all suggest that the formation of a channel-inactive desensitized state results predominantly from a conformational change in solvent-accessible extramembranous regions of the polypeptide backbone as opposed to a large structural perturbation near the ion channel gate. A conformational change in the agonist binding site may be primarily responsible for channel inactivation upon desensitization.