Kotani S, Ikai A, Kawai G, Maekawa S, Yokoyama S, Sakai H
Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Japan.
Eur J Biochem. 1988 Oct 1;176(3):573-80. doi: 10.1111/j.1432-1033.1988.tb14316.x.
Microtubule-assembly inhibitor protein (MIP) is an acidic protein with Mr 33,000 which inhibits microtubule assembly in vitro [Kotani, S., Murofushi, H., Nishida, E. & Sakai, H. (1984) J. Biochem. (Tokyo) 96, 959-969]. Anti-MIP antibody was affinity-purified from rabbit anti-MIP sera raised against chemically modified MIP. MIP was localized in the nucleus in interphase culture cells as revealed by immunofluorescent light microscopy. Immunoblotting experiments showed that MIP exists in a variety of mammalian cells and tissues. Kidney appeared to be a better source of MIP than brain, the original source. Kidney MIP was isolated by the same procedure as for brain MIP and proved to be indistinguishable from brain MIP in the inhibitory activity of microtubule assembly, molecular mass, immunoreactivity, and one-dimensional peptide mapping. Physico-chemical characteristics of MIP were studied using the kidney protein. It contained 20% aspartic acid and 25% glutamic acid, accounting for its acidic nature. Hydrodynamically, MIP was a monomer with S20,w = 1.9 S and Mr = 30,000. The frictional ratio, f/fo = 1.7, indicated that MIP is not a globular molecule but has either an elongated or an expanded structure. Circular dichroic results showed a low content of alpha-helix or beta-sheet structure for MIP. Proton nuclear magnetic resonance analysis provided evidence that MIP consists mainly of very flexible structures (random-coil-like structures), but still contains a hydrophobic core structure below 60 degrees C.
微管组装抑制蛋白（MIP）是一种酸性蛋白，分子量为33000，可在体外抑制微管组装[小谷，S.，室伏，H.，西田，E. & 酒井，H.（1984年）《生物化学杂志》（东京）96，959 - 969]。抗MIP抗体是从针对化学修饰的MIP产生的兔抗MIP血清中亲和纯化得到的。免疫荧光显微镜显示，MIP定位于间期培养细胞的细胞核中。免疫印迹实验表明，MIP存在于多种哺乳动物细胞和组织中。肾脏似乎比原始来源脑是更好的MIP来源。肾脏MIP通过与脑MIP相同的程序分离，并且在微管组装抑制活性、分子量、免疫反应性和一维肽图谱方面被证明与脑MIP没有区别。使用肾脏蛋白研究了MIP的物理化学特性。它含有20%的天冬氨酸和25%的谷氨酸，这解释了它的酸性性质。从流体动力学角度看，MIP是一种单体，S20,w = 1.9 S，分子量为30000。摩擦系数f/fo = 1.7，表明MIP不是球形分子，而是具有伸长或扩展的结构。圆二色性结果显示MIP的α - 螺旋或β - 折叠结构含量较低。质子核磁共振分析提供了证据，表明MIP主要由非常灵活的结构（类似无规卷曲的结构）组成，但在60摄氏度以下仍含有疏水核心结构。
