Single particle reconstruction

In physics, in the area of microscopy, single particle reconstruction is a technique in which large numbers of images (10,000 - 1,000,000) of ostensibly identical individual molecules or macromolecular assemblies are combined to produce a 3 dimensional reconstruction. This is a complementary technique to crystallography of biological molecules. As molecules/assembies become larger, it becomes more difficult to prepare high resolution crystals. For single particle reconstruction, the opposite is true. Larger objects actually improve the resolution of the final structure. In single particle reconstruction, the molecules/assemblies in solution are prepared in a thin layer of vitreous (glassy) ice, then imaged on an electron cryomicroscope (see Transmission electron microscopy). Images of individual molecules/assemblies are then selected from the micrograph and then a complex series of algorithms is applied to produce a full volumetric reconstruction of the molecule/assembly. In the 1990s this technique was limited to roughly 2 nm resolution, providing only gross features of the objects being studied. However, recent improvements in both microscope technology as well as available computational capabilities now make 0.5 nm resolution possible.