The structures of trypanosome surface proteins.
A. The structures of the major surface proteins of the T. congolense epimastigote, the glutamic acid rich protein (GARP) and of the T. brucei bloodstream form, the variant surface glycoprotein (VSG), and the structures of the T. brucei and T. congolense haptoglobin–hemoglobin receptors (TbHpHbR and TcHpHbR). Both TbHpHbR and TbVSG are elongated by additional C-terminal domains, which are not represented . B. The structure of a complex of two TcHpHbR bound to a single hemoglobin tetramer. The receptors are coupled to the cell membrane by a GPI anchor and will tilt in order to simultaneously bind to a single hemoglobin. C. The structure of a complex of two TbHpHbR bound to a haptoglobin–hemoglobin tetramer (silver and gold), showing how the kink in the receptor allows two membrane-linked TbHpHbR to simultaneously bind to a single HpHb.