Domain-swapped dimer structure in the crystal and reconstituted monomer structure of the MBP-sAglB fusion protein. (A) Two MBP-sAglB molecules form a symmetric intertwined dimer, in which the molecules are related by a crystallographic 2-fold axis. The two molecules in the dimer structure are colored pink/magenta and blue/cyan. The hinge loop region is colored green. The dashed lines indicate the missing residues in the final model. (B) Close-up view of the hinge loop region (box, in A) with an Fo-Fc omit map contoured at +3σ. The simulated omit map was calculated by deleting residues 566–574, (C) Reconstituted monomeric structure of the C-terminal domain of Af AglB-L. The 73 residues from one molecule (Af AglB-L-N), and the 296 residues from another molecule (Af AglB-L-C), related by a 2-fold axis in the crystal, are colored magenta and cyan, respectively. The swapping site between Ala572 and Gly573 is shown as dashed lines between the two green spheres. (D) Stereo view of the reconstituted model of the C-terminal domain of Af AglB-L. The side chains of the WWDYG motif are labeled and colored yellow. The backbone of the WWDYG motif and following α-helix and loop are colored pink. The characteristic kinked helix is colored light brown, and the side chains of the first and second signature residues, E613 and K618, constituting the DK motif on the characteristic kinked helix are labeled and colored green. The amino acid sequence inserted in the DK motif is colored magenta. The cluster of three α-helices, are labeled as αA, αB, and αC, and colored yellow-green. The two pink spheres show the swapping site. The figures in (C) and (D) are related by a 90 degrees rotation about the vertical axis.