title: Electron microscopy and image processing: an essential tool for structural analysis of macromolecules.
abstract: Macromolecular electron microscopy (EM) deals with macromolecular complexes and their placement within the cell-linking the molecular and cellular worlds as a bridge between atomic-resolution X-ray crystallographic or NMR studies and lower resolution light microscopy. The amount of specimen required is typically 10(2) to 10(3) times less than for X-ray crystallography or NMR. Electron micrographs of frozen-hydrated specimens portray native structures. Computer averaging yields enhanced images with reduced noise. Three-dimensional reconstructions may be computed from multiple views. Under favorable circumstances, resolutions of 7 to 10 A are achieved. Fitting atomic-resolution coordinates of components into three-dimensional density maps gives pseudo-atomic models of a complex's structure and interactions. Time-resolved experiments describe conformational changes. Electron tomography allows reconstruction of pleiomorphic complexes and sub-cellular structures. Electron crystallography has produced near-atomic resolution models of two-dimensional arrays, notably of membrane proteins.
authors.affiliation: NIAMS/NIH, Bethesda, Maryland.
authors.forename: Alasdair
authors.initials: A
authors.lastname: Steven
authors.affiliation: Department of Chemistry and Biochemistry Brigham Young University, Provo, Utah.
authors.forename: David
authors.initials: D
authors.lastname: Belnap
mesh_terms: D001704:Biopolymers / Q000737:chemistry; D003460:Crystallization; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D046911:Macromolecular Substances / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry; D008854:Microscopy, Electron / Q000379:methods*; D015394:Molecular Structure; D015203:Reproducibility of Results
chemical_list: D001704:Biopolymers; D046911:Macromolecular Substances; D008565:Membrane Proteins