Xu G Z, Shi B, McGroarty E J, Tien H T
Biochim Biophys Acta. 1986 Nov 6;862(1):57-64. doi: 10.1016/0005-2736(86)90468-2.
The opening and closing of the ompF porin from Escherichia coli JF 701 was investigated by reconstituting the purified protein into planar bilayer membranes. The electrical conductance changes across the membranes at constant potential were used to analyze the size and aggregate nature of the porin channel complexes and the relative number of opening and closing events. We found that, when measured at pH 5.5, the channel conductance diminished and the number of closing events increased when the voltage was greater than 100 mV. The results suggest that the number of smaller sized conductance channels increases above this potential. There was also an increase in the smaller subunits and in the closing events when the pH was lowered to 3.5, and these changes were further enhanced by increasing the voltage. We propose that both lowering the pH and elevating the potential across the membrane stabilize the porin in a conformation in which the subunits are less tightly associated and the subunits open in a non-cooperative manner. These same conditions also appear to stabilize the closed state of the pore.
通过将纯化的蛋白质重组到平面双层膜中，研究了来自大肠杆菌JF 701的ompF孔蛋白的开闭情况。利用恒定电位下跨膜的电导变化来分析孔蛋白通道复合物的大小和聚集性质，以及开闭事件的相对数量。我们发现，在pH 5.5下测量时，当电压大于100 mV时，通道电导降低，关闭事件的数量增加。结果表明，高于此电位时，较小尺寸电导通道的数量增加。当pH降至3.5时，较小亚基的数量和关闭事件也增加，并且通过增加电压，这些变化进一步增强。我们提出，降低pH和提高跨膜电位都能使孔蛋白稳定在一种构象中，在这种构象中，亚基之间的结合不那么紧密，亚基以非协同方式打开。这些相同的条件似乎也能稳定孔的关闭状态。
