Figure 3.

αCTD^M crystal packing. (a) The content of one complete P2₁ unit cell (two crystal asymmetric units with eight αCTD^M protomers per asymmetric unit) is shown with the unit cell outlined in green. For reference, one protomer is identified with rainbow coloring (blue, N-terminus; red, C-terminus). The pale red arrow indicates the approximate translational symmetry that gives rise to the Patterson map u = 0, v = 0, w = ½ pseudo-translation vector. (b) αCTD^M crystallographic dimer; a sodium ion positioned at the dimer interface is shown in pink. (c) Metal-ion-binding site formed by αCTD^M C-termini at the center of the crystal dimer. O atoms are colored red; N atoms are colored blue; Trp321–Pro322 cis-peptide bonds are colored cyan.