Interaction mechanisms between polyamines and IRK1 inward rectifier K+ channels.
Interaction mechanisms between polyamines and IRK1 inward rectifier K+ channels.
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DOI：
10.1085/jgp.200308890
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发表时间：
2003-11
影响因子：
3.8
通讯作者：
Lu, Zhe
中科院分区：
文献类型：
--
作者：
Guo, Donglin;Lu, Zhe
宏观电流通过内向整流钾（Kir）通道的整流反映了细胞内阳离子如多胺对通道阻滞的强烈电压依赖性。电压依赖性主要来自跨膜电场中K+离子的运动，这伴随着阻断剂的结合-解结合。IRK 1中的残基D172、E224和E299对于阻断剂的高亲和力结合至关重要。D172似乎位于狭窄的K+选择性过滤器的内部，而E224和E299在更细胞内的位点形成环。使用一系列不同长度的烷基双胺作为校准，我们研究了IRK 1中的酸性残基如何与天然多胺（腐胺，亚精胺和精胺）中引起细胞整流的胺基相互作用。为了阻断孔，增加长度的双胺的前导胺朝向D172更深地渗透到孔中，而每个双胺中的尾随胺在更细胞内的位点附近结合并与E224和E299相互作用。在九亚甲基双胺（bis-C9）中的前导胺最接近D172，置换了最大数量的K+离子，并表现出最强的电压依赖性。细胞不会合成比腐胺（bis-C4）更长的双胺，但通过将氨基丙基连接到腐胺的一端或两端来产生多胺亚精胺和精胺。通过四胺精胺的通道阻断的电压依赖性与通过双胺bis-C9（较短）或bis-C12（等长）的通道阻断的电压依赖性相当，但是精胺以比任一双胺高得多的亲和力结合IRK 1。因此，与直觉相反，精胺中的多种胺主要赋予通道阻断的高亲和力而不是强电压依赖性。四价精胺通过有效地表现得像一对拴系的二价阳离子而与孔实现更强的相互作用，其前半部分中的两个胺基主要与D172相互作用，而后半部分中的另外两个主要与E224和E299相互作用。因此，自然界不仅优化了阻断剂，而且以互补的方式优化了通道，以产生快速、高亲和力和强烈的电压依赖性通道阻断，从而产生非常急剧的整流。
Rectification of macroscopic current through inward-rectifier K+ (Kir) channels reflects strong voltage dependence of channel block by intracellular cations such as polyamines. The voltage dependence results primarily from the movement of K+ ions across the transmembrane electric field, which accompanies the binding–unbinding of a blocker. Residues D172, E224, and E299 in IRK1 are critical for high-affinity binding of blockers. D172 appears to be located somewhat internal to the narrow K+ selectivity filter, whereas E224 and E299 form a ring at a more intracellular site. Using a series of alkyl-bis-amines of varying length as calibration, we investigated how the acidic residues in IRK1 interact with amine groups in the natural polyamines (putrescine, spermidine, and spermine) that cause rectification in cells. To block the pore, the leading amine of bis-amines of increasing length penetrates ever deeper into the pore toward D172, while the trailing amine in every bis-amine binds near a more intracellular site and interacts with E224 and E299. The leading amine in nonamethylene-bis-amine (bis-C9) makes the closest approach to D172, displacing the maximal number of K+ ions and exhibiting the strongest voltage dependence. Cells do not synthesize bis-amines longer than putrescine (bis-C4) but generate the polyamines spermidine and spermine by attaching an amino-propyl group to one or both ends of putrescine. Voltage dependence of channel block by the tetra-amine spermine is comparable to that of block by the bis-amines bis-C9 (shorter) or bis-C12 (equally long), but spermine binds to IRK1 with much higher affinity than either bis-amine does. Thus, counterintuitively, the multiple amines in spermine primarily confer the high affinity but not the strong voltage dependence of channel block. Tetravalent spermine achieves a stronger interaction with the pore by effectively behaving like a pair of tethered divalent cations, two amine groups in its leading half interacting primarily with D172, whereas the other two in the trailing half interact primarily with E224 and E299. Thus, nature has optimized not only the blocker but also, in a complementary manner, the channel for producing rapid, high-affinity, and strongly voltage-dependent channel block, giving rise to exceedingly sharp rectification.