There are several ways to superimpose structures in Chimera:
•  MatchMaker performs a fit after automatically identifying which residues should be paired. Pairing uses both sequence and secondary structure, allowing similar structures to be superimposed even when their sequence similarity is low to undetectable.
The figure shows five distantly related proteins (pairwise sequence identities <25%) from the SCOP WD40 superfamily before and after MatchMaker superposition with default parameters.
•  Structures can be matched using a pre-existing sequence alignment.
•  The exact atoms to pair can be specified with the match command. This works on any type of structure, while the preceding methods apply only to peptide and nucleotide chains.
•  Structures can be superimposed manually by activating/deactivating them for motion and using the mouse.

Mutations that inactivate the tumor suppressor p53 are found in over 50% of human cancers, and most of the cancer-associated mutations are within its DNA-binding domain. The image shows a tetramer of the p53 DNA-binding domain complexed with DNA (Protein Data Bank entry 2ac0). The tetramer subunits are shown as light blue, green, orange, and yellow ribbons, with red spheres marking several major "hot spots" of mutation. The DNA is shown in purple and blue. (More samples...)