Kinesin undergoes a 9 S to 6 S conformational transition.
Kinesin undergoes a 9 S to 6 S conformational transition.
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DOI：
10.1016/s0021-9258(18)42499-4
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发表时间：
1992-04
期刊：
影响因子：
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通讯作者：
D. Hackney;J. D. Levitt;J. Suhan
中科院分区：
文献类型：
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作者：
D. Hackney;J. D. Levitt;J. Suhan
在50 nM ATP存在下，NaCl或KCl的加入使酪蛋白的沉降系数（表观S20，w）从低离子强度下的9.4 S转变为高离子强度下的6.5 S。当pH值分别为6.3、6.9和8.3时，离子强度分别为0.39、0.25和0.18时，发生转变的中点。凝胶过滤实验表明，向6.5 S的过渡伴随着扩散系数的降低。在所有测试条件下，64-kDa β亚基与120-kDa α亚基同源，没有任何证据表明α 2 β 2复合物的解离。这些结果与沉积系数的变化是由于低离子强度下的折叠形式和高离子强度下的扩展形式之间的构象转变一致。这种构象转变不受结合在活性位点的核苷酸的性质的显著影响，因为在过量EDTA存在的情况下，去除结合的ADP，以及在用5'-（β， γ -亚胺）三磷酸腺苷取代结合的ADP后，都得到了类似的结果。缺少β亚基的α - 2形式的酪蛋白在低离子强度下的6.7 S形式和高离子强度下的5.1 S形式之间经历了类似的转变，在pH值为6.9的离子强度为0.5时发生转变。电镜观察还表明，α 2 β 2和α 2两种物质在低离子强度的折叠构象和高离子强度的扩展构象之间发生转变。
Addition of NaCl or KCl in the presence of 50 nM ATP induces a shift in the sedimentation coefficient (apparent S20,w) of kinesin from 9.4 S at low ionic strength to 6.5 S at high ionic strength. The midpoint for the transition occurs at ionic strength values of 0.39, 0.25, and 0.18 for pH values of 6.3, 6.9, and 8.3, respectively. Gel filtration experiments indicate that the transition to the 6.5 S species is accompanied by a decrease in the diffusion coefficient. Under all conditions which were tested, the 64-kDa beta subunits comigrate with the 120-kDa alpha subunits without any evidence for dissociation of the alpha 2 beta 2 complex. These results are consistent with the change in sedimentation coefficient being due to a conformational transition between a folded form at low ionic strength and an extended form at high ionic strength. This conformational transition is not significantly affected by the nature of the nucleotide bound at the active site since similar results are obtained both in the presence of excess EDTA, which removes the bound ADP, and after replacement of the bound ADP with adenosine 5'-(beta,gamma-imino)triphosphate. The alpha 2 form of kinesin, which lacks the beta subunits, undergoes a similar transition between a 6.7 S form at low ionic strength and a 5.1 S form at high ionic strength with a midpoint for the transition at an ionic strength of 0.5 at pH 6.9. Electron microscopic observation also indicates a transition between a folded conformation at low ionic strength and an extended conformation at high ionic strength for both the alpha 2 beta 2 and alpha 2 species.