生物三维电子显微学进入全新高速发展时期

THREE-DIMENSIONAL ELECTRON MICROSCOPY IN BIOLOGY ENTERS A PERIOD OF RAPID DEVELOPMENT AND WIDESPREAD APPLICATIONS

生物三维电子显微学主要由三个部分组成——电子晶体学、单颗粒技术和电子断层成像术,其结构解析对象的尺度范围介于X射线晶体学与光学显微镜之间,适合从蛋白质分子结构到细胞和组织结构的解析。以冷冻电镜技术与三维重构技术为基础的低温电子显微学代表了生物电子显微学的前沿。低温单颗粒技术对于高度对称的病毒颗粒的解析最近已达到3.8"分辨率,正在成为解析分子量很大的蛋白质复合体高分辨结构的有效技术手段。低温电子断层成像技术目前对于真核细胞样品的结构解析已达到约40#的分辨率,在今后5年有望达到20$。这样,把X射线晶体学、NMR以及电镜三维重构获得的蛋白质分子及复合体的高分辨率的结构,锚定到较低分辨率的电子断层成像图像中,从而在细胞水平上获得高精确的蛋白质空间定位和原子分辨率的蛋白质相互作用的结构信息。这将成为把分子水平的结构研究与细胞水平的生命活动衔接起来的可行途径。

Three-dimensional biological electron microscopy includes three major aspects:electron crystallography,single particle analysis and electron tomography.The size range of the objects resolved by electron microscopy falls between X-ray crystallography and light microscopy,which coveres anything from the structures of protein molecules to the structures of cells and tissues.Cryo-electron microscopy,based upon a combination of cryo-techniques and three dimensional reconstruction methods,represents the frontier of current biological electron microscopy.Using the cryo-single particle technique,the resolution of a virus structure having high symmetry has recently reached to 3.8 A,indicating this technique is becoming effective in solving structures to high resolution,particularly those of large protein complexes.Using cryo-electron tomography,the resolution of eukaryotic cells has reached to around 40 A and,with confidence,is expected to approach to 20 A in 5 years.Thus,by docking the high-resolution component structures obtained from X-ray,NMR and cryo-electron crystallography into the low resolution images obtained by cryo-electron tomography,we can gain high positional accuracy of the components in cells and therefore reach to atomic resolution for subcellular structures.This will become a practical approach to build a link between the component structures at molecular level and the biological functions at the cell level.