LOCATION OF ION-BINDING SITES IN THE GRAMICIDIN CHANNEL BY X-RAY-DIFFRACTION
LOCATION OF ION-BINDING SITES IN THE GRAMICIDIN CHANNEL BY X-RAY-DIFFRACTION
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DOI：
10.1016/0022-2836(91)90272-8
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发表时间：
1991-04-20
影响因子：
5.6
通讯作者：
WU, YL
中科院分区：
文献类型：
--
作者：
OLAH, GA;HUANG, HW;WU, YL
我们通过使用含有短杆菌肽和离子（Tl+、K+、Ba2+、Mg2+ 或不含离子）的均匀排列的多层膜样品，首次报道了膜活性形式的短杆菌肽的 X 射线衍射。根据不同的电子密度分布，我们在距短杆菌肽通道中点 9.6(±0.3) Å 处发现了一对对称分布的 Tl+ 离子结合位点，在距离短杆菌肽通道中点 13.0(±0.2) Å 处有一对对称分布的 Ba2+ 离子结合位点。 Ba2+结合位点的位置靠近通道末端，这与二价阳离子不渗透而是阻塞通道的实验观察结果一致。 Tl+结合位点的位置有点令人惊讶。人们普遍认为单价阳离子从通道口结合到螺旋的第一圈。 （现在普遍认为，短杆菌肽通道是由两个单体形成的圆柱形孔，每个单体都是单链β6.3螺旋，并且在它们的N末端头对头地形成氢键。）但是我们的实验表明，Tl+结合位点要么靠近第一个螺旋转角的底部，要么位于第一个螺旋转角的下方。
We report the first X-ray diffraction on gramicidin in its membrane-active form by using uniformly aligned multilayer samples of membranes containing gramicidin and ions (Tl+, K+, Ba2+, Mg2+or without ions). Prom the difference electron density profiles, we found a pair of symmetrically located ion-binding sites for Tl+at 9.6(±0.3) Å and for Ba2+at 13.0(±0.2) Å from the midpoint of the gramicidin channel. The location of Ba2+-binding sites is near the ends of the channel, consistent with the experimental observation that divalent cations do not permeate but block the channel. The location of Tl+-binding sites is somewhat of a surprise. It was generally thought that monovalent cations bind to the first turn of the helix from the mouth of the channel. (It is now generally accepted that the gramicidin channel is a cylindrical pore formed by two monomers, each a single-strandedβ6.3helix and hydrogen-bonded head-to-head at their N termini.) But our experiment shows that the Tl+-binding site is either near the bottom of or below the first helix turn.