A: Topology of YHI9 showing the bimodular structure of the protein (figure made by Tops[26]). Each domain comprises about half of the protein. The -sheets of the N-terminal and C-terminal domains are colored red and blue respectively. The two -strands involved in domain swapping (9) are colored purple. The helical insertions common to the two domains are in orange (1, 2) and the supplementary helices in domain b are colored green (3b, 4b). B: Superposition of the N-terminal (red) and C-terminal (blue) domains of YHI9. C: Ribbon representation of YHI9 (left). The color code is the same as for (A). For clarity, only a few prominent secondary structure elements are labelled. The 120° angle between the axes of the two barrels is highlighted in dotted lines. Molecular surface colored in increasing tones of red corresponding to increasing surface residue conservation (right), calculated with the 50 proteins of highest sequence homology determined by the Consurf server.[27] D: Ribbon (left) and molecular surface (right) representation of YHI9, perpendicular view in respect to (C). Residues of the putative catalytic site [detailed in Fig. 3(A)] are shown in stick representation. E: Representation of the dimer of YHI9 generated by crystal symmetry.