Anisotropic B-factors can be shown as ellipsoids, with ellipsoid axes and radii representing the eigenvectors and eigenvalues of the atomic mean-square displacement matrix. Anisotropic B-factors are read from the input coordinate file (for example, from ANISOU records in a PDB file) and can be displayed with the tool Thermal Ellipsoids or the command aniso. The figure shows ellipsoids scaled to enclose 50% probability for the heme and nearby atoms from PDB entry 1a6m.

The image shows the structure of the human TRPA1 ion channel (wasabi receptor) determined by electron cryo-microscopy, Protein Data Bank entry 3j9p. The four subunits of the tetramer are shown as ribbons in different colors over a dark-to-light gradient background. (More samples...)