Figure 1.

Structure of the isolated C-domain from P140. (a) Two views (90° apart from each other) of the structure of one subunit of the C-domain from P140 as found in the asymmetric unit of the tetragonal crystals. The three strands in the β-sheet are indicated. The third strand is interrupted by an insertion of ten residues that is partially disordered. The positions of an Na⁺ ion and a Cl⁻ ion are also depicted. (b) Two views, 90° apart, down and perpendicular to the fourfold axis, of the octamer with D4 symmetry found in the asymmetric unit of the monoclinic crystals. (c) In spite of the differences in the unit-cell content, the structures of the subunits and the packing interactions are similar in both the tetragonal (I422, upper panels, with one subunit in the asymmetric unit shown in red) and the monoclinic (C2, lower panels, with a whole octamer shown in color) crystals.