Evans P R, Farrants G W, Lawrence M C
J Mol Biol. 1986 Oct 20;191(4):713-20. doi: 10.1016/0022-2836(86)90455-9.
The structure of the allosterically inhibited form of phosphofructokinase from Bacillus stearothermophilus has been determined by X-ray crystallography to 7 A resolution by molecular replacement using the known structure of the active state as a starting model. Comparing the inhibited state with the active state, the tetramer is twisted about its long axis such that one pair of subunits in the tetramer rotates relative to the other pair by about 8 degrees around one of the molecular dyad axes. This rotation partly closes the binding site for the co-operative substrate fructose-6-phosphate, explaining its weaker binding to this conformational state. Within the subunit, one domain rotates relative to the other by 4.5 degrees, which further closes the fructose-6-phosphate site, without closing the cleft between the domains of the same subunit: this motion causes little change to the catalytic site. This T-state model is consistent with the simple allosteric kinetic scheme in which the active and the inhibited conformations differ in their affinities for fructose-6-phosphate, but not in their catalytic rates. It does not explain the heterotropic allosteric effects.
嗜热栖热芽孢杆菌磷酸果糖激酶变构抑制形式的结构已通过X射线晶体学以7埃的分辨率测定，采用活性状态的已知结构作为起始模型，通过分子置换法完成。将抑制状态与活性状态进行比较，四聚体围绕其长轴扭曲，使得四聚体中的一对亚基相对于另一对亚基围绕分子二分轴之一旋转约8度。这种旋转部分关闭了协同底物6-磷酸果糖的结合位点，解释了其与这种构象状态的较弱结合。在亚基内，一个结构域相对于另一个结构域旋转4.5度，这进一步关闭了6-磷酸果糖位点，但没有关闭同一亚基结构域之间的裂隙：这种运动对催化位点几乎没有影响。这种T态模型与简单的变构动力学方案一致，在该方案中，活性和抑制构象对6-磷酸果糖的亲和力不同，但催化速率相同。它无法解释异促变构效应。
