Homology model of T. congolense TS1. The crystal structure of T. cruzi TS  in complex with 3-fluoro-5-N-acetyl-9-benzamido-2,9-dideoxy-neuraminic acid was used as template to calculate a model structure for T. congolense TS1 e-1. Only the Neu5Ac part (orange) of the ligand in the binding site of the complex is illustrated. (A) Conserved amino acids of the active site are labeled in white. Amino acids at positions reported to be important for ligand binding in T. cruzi TS , which are not conserved in T. congolense are labeled in yellow. The red labeled position 407 is a serine or valine in T. congolense TS1 forms. R144, which is exchanged to a cysteine in TS1g, is labeled in blue. (B) Green clouds mark positions at which different amino acids occur in other T. congolense TS1 forms.