A Fo-Fc omit map of ADP and TPO68. The map was contoured at 2.5 σ level. ADP, TPO68 of SaiC and Asn65 of SiaB are shown as sticks. Na+ ion is shown as black sphere. B Surface presentation of the ADP binding pocket. C Detailed interactions between ADP and SiaB. ADP and the interacting residues are shown as sticks. 