Hirokawa Nobutaka
Department of Cell Biology and Anatomy, Graduate School of Medicine, University of Tokyo, Hongo, 7-3-1, Bunkyo-ku, Tokyo, Japan 113-0033.
J Electron Microsc (Tokyo). 2011;60 Suppl 1:S63-92. doi: 10.1093/jmicro/dfr051.
Cells transport and sort various proteins and lipids following synthesis as distinct types of membranous organelles and protein complexes to the correct destination at appropriate velocities. This intracellular transport is fundamental for cell morphogenesis, survival and functioning not only in highly polarized neurons but also in all types of cells in general. By developing quick-freeze electron microscopy (EM), new filamentous structures associated with cytoskeletons are uncovered. The characterization of chemical structures and functions of these new filamentous structures led us to discover kinesin superfamily molecular motors, KIFs. In this review, I discuss the identification of these new structures and characterization of their functions using molecular cell biology and molecular genetics. KIFs not only play significant roles by transporting various cargoes along microtubule rails, but also play unexpected fundamental roles on various important physiological processes such as learning and memory, brain wiring, development of central nervous system and peripheral nervous system, activity-dependent neuronal survival, development of early embryo, left-right determination of our body and tumourigenesis. Furthermore, by combining single-molecule biophysics with structural biology such as cryo-electrom microscopy and X-ray crystallography, atomic structures of KIF1A motor protein of almost all states during ATP hydrolysis have been determined and a common mechanism of motility has been proposed. Thus, this type of studies could be a good example of really integrative multidisciplinary life science in the twenty-first century.
细胞在合成各种蛋白质和脂质后，会将它们作为不同类型的膜性细胞器和蛋白质复合物，以适当的速度运输并分类到正确的目的地。这种细胞内运输不仅对于高度极化的神经元，而且对于一般所有类型的细胞的形态发生、存活和功能都是至关重要的。通过开发快速冷冻电子显微镜（EM），发现了与细胞骨架相关的新丝状结构。对这些新丝状结构的化学结构和功能的表征使我们发现了驱动蛋白超家族分子马达KIFs。在这篇综述中，我将讨论这些新结构的鉴定以及使用分子细胞生物学和分子遗传学对其功能的表征。KIFs不仅通过沿着微管轨道运输各种货物发挥重要作用，而且在各种重要的生理过程中也发挥着意想不到的基础作用，如学习和记忆、脑布线、中枢神经系统和外周神经系统的发育、活动依赖性神经元存活、早期胚胎发育、身体的左右决定以及肿瘤发生。此外，通过将单分子生物物理学与冷冻电子显微镜和X射线晶体学等结构生物学相结合，已经确定了ATP水解过程中几乎所有状态的KIF1A运动蛋白的原子结构，并提出了一种共同的运动机制。因此，这类研究可能是21世纪真正综合的多学科生命科学的一个很好的例子。
