Kooijman M, Bloemendal M, van Amerongen H, Traub P, van Grondelle R
Department of Biophysics, Free University, Amsterdam, The Netherlands.
J Mol Biol. 1994 Mar 4;236(4):1241-9. doi: 10.1016/0022-2836(94)90024-8.
In this work we have studied the structure of soluble vimentin units from which intermediate filaments (IFs) are built. Several oligomeric forms have been presented in the literature as IF "building blocks", but there is still no agreement on this matter. By comparing our data with various models as proposed in the literature we can favour certain models and reject others. Transient electric birefringence (TEB) measurements were performed from which information is obtained concerning electric and hydrodynamic properties of the particles under investigation. TEB decay analysis at pH 6.8 after 70 microseconds pulses (at 20 degrees C in aqueous solution) yielded three decay times: 1.1(+/- 0.3) microseconds, 4.0(+/- 1.0) microseconds and 20.0(+/- 5.0) microseconds, with amplitudes of 45% to 60%, 30% to 45%, and less than 10%, respectively. At pH 8.5 after 70 microseconds pulses, more than 90% of the TEB signal with the second decay time is obtained, while the remainder had a decay time of 15.0(+/- 4.0) microseconds. Only when the pulse duration was decreased, the fast decay time around 1 microsecond was observed, suggesting that only a minor fraction of the particles at this pH value causes such a short decay time. At both pH values, the TEB measurements indicated that, at least in part, the molecules are oriented by a permanent dipole moment. It will be shown that the shortest decay time originates from bent or flexible dimers, and the second decay time from particles with a length of 54 to 65 nm containing, at least in part, a relatively large overall dipole moment. The longest decay time is probably due to larger aggregates. These results are consistent with a model in which single dimers, antiparallel staggered tetramers and hexamers coexist. Alternatively, but less likely on the basis of literature data, a model of parallel in-register tetramers with a considerable length contribution of the head groups would fit our research.
在这项工作中，我们研究了构成中间丝（IFs）的可溶性波形蛋白单元的结构。文献中提出了几种寡聚形式作为IF的“构建块”，但在这个问题上仍未达成共识。通过将我们的数据与文献中提出的各种模型进行比较，我们可以支持某些模型并否定其他模型。进行了瞬态电双折射（TEB）测量，从中获得了有关所研究颗粒的电学和流体动力学性质的信息。在70微秒脉冲后（在20℃的水溶液中，pH值为6.8）进行的TEB衰减分析产生了三个衰减时间：1.1（±0.3）微秒、4.0（±1.0）微秒和20.0（±5.0）微秒，其幅度分别为45%至60%、30%至45%和小于10%。在pH值为8.5、70微秒脉冲后，获得了超过90%具有第二个衰减时间的TEB信号，而其余部分的衰减时间为15.0（±4.0）微秒。只有当脉冲持续时间缩短时，才观察到约1微秒的快速衰减时间，这表明在该pH值下只有一小部分颗粒会导致如此短的衰减时间。在这两个pH值下，TEB测量表明，至少部分分子是由永久偶极矩定向的。结果将表明，最短的衰减时间源自弯曲或柔性二聚体，第二个衰减时间源自长度为54至65nm的颗粒，这些颗粒至少部分包含相对较大的整体偶极矩。最长的衰减时间可能归因于更大的聚集体。这些结果与单二聚体、反平行交错四聚体和六聚体共存的模型一致。或者，根据文献数据可能性较小的是，一种平行对齐四聚体模型，其头部基团对长度有相当大的贡献，也符合我们的研究。
