Overall structure of triclinic azurin T21R1 crystals. A) The asymmetric unit. The four azurin chains (I-IV) are depicted as cartoon models; the R1 side chains are shown as sticks. Brown spheres mark the positions of the copper ions. The two-fold NCS symmetry axis is indicated and the monomers are coloured to emphasize the NCS relationship. B) Superposition of all four monomers (colouring is identical to panel A). C) Superposition of monomer I with a previously published structure of azurin (magenta, PDB-ID: 1E67, ).