A The overall fold of SiaB/SiaC complex. The two SiaB molecules are shown as cartoons in light blue and pink, respectively. The two SiaC molecules are all shown as cartoons in yellow. ADP and TPO68 are shown as spheres in atomic colors (C, cyan; N, blue; O, red; P, orange). B Detailed interactions between SiaB and SiaC. The interacting residues are showing as sticks. The C-atoms of SiaB and SiaC residues are colored in light blue and yellow, respectively. H-bonds are indicated by black dashed lines. 