Comparison of Ub crystallographic dimers. Monomer A of Ub (in green, this work) was superimposed with one monomer of either 1AAR, 2O6V, 1F09, 2JF5, 1TBE. Only the α-carbon traces are displayed. The monomer B of Ub is in cyan, while the A and B monomers of other ubiquitins are colored in red and magenta. When present, cadmium ions from the crystallization media are shown as spheres.