Kooijman M, Bloemendal M, Traub P, van Grondelle R, van Amerongen H
Department of Biophysics, Free University, Amsterdam, The Netherlands.
J Biol Chem. 1995 Feb 17;270(7):2931-7. doi: 10.1074/jbc.270.7.2931.
The structure and charge distribution of T-vimentin, which differs from the intact intermediate filament protein vimentin through the absence of the first 70 amino acids, has been studied by transient electric birefringence measurements. It is found that in 0.7 mM phosphate, pH 7.5 buffer, exclusively single dimers (with a hydrodynamic length of 40 to 43 nm) are present, which are considerably bent and/or flexible and which have a relatively large permanent dipole moment. This indicates a parallel alignment of two protein chains. In 0.2 mM phosphate, 0.5 mM MgCl2, pH 7.5, predominantly tetrameric T-vimentin is found with a rigid structure, no permanent dipole moment, and a length of 63 to 68 nm. Tetramer formation is likely to be induced by binding of Mg2+ to the protein. The observed length is in agreement with that of intact vimentin tetramers in which the 1B regions of the rod domains of the dimers overlap (A11 configuration). A minor part of the tetramers may be in a flexible or bent A22 form. The loss of the permanent dipole moment when tetramers are formed is, apart from charge compensation, presumably due to the antiparallel alignment of the constituting dimers in which their dipoles cancel.
波形蛋白前70个氨基酸缺失，从而形成了T-波形蛋白。通过瞬态电双折射测量研究了T-波形蛋白的结构和电荷分布。发现在pH 7.5的0.7 mM磷酸盐缓冲液中，仅存在单二聚体（流体动力学长度为40至43 nm），这些二聚体明显弯曲和/或具有柔韧性，并且具有相对较大的永久偶极矩。这表明两条蛋白质链呈平行排列。在pH 7.5的0.2 mM磷酸盐、0.5 mM氯化镁中，主要发现具有刚性结构、无永久偶极矩且长度为63至68 nm的四聚体T-波形蛋白。四聚体的形成可能是由Mg2+与蛋白质结合诱导的。观察到的长度与完整波形蛋白四聚体的长度一致，其中二聚体杆状结构域的1B区域重叠（A11构型）。一小部分四聚体可能呈柔性或弯曲的A22形式。形成四聚体时永久偶极矩的丧失，除了电荷补偿外，大概是由于构成二聚体的反平行排列，其中它们的偶极相互抵消。
