Haptoglobin-hemoglobin receptor (HpHbR), a protein found within the variant surface glycoprotein (VSG) from trypanosomes, plays a key role in determining if humans can be infected by these parasites developing sleeping sickness. HpHbR is responsible for the acquisition of haem, an important growth factor for these organism that are deficient in its biosynthesis. This protein folds into an elongated three alpha-helical bundle with a small head structure containing the ligand-binding site that is distal to the C-terminal GPI-anchor attachment site. This structure appears to be conserved among trypanosome species [1-4].

1: Structure of the trypanosome haptoglobin-hemoglobin receptor and implications for nutrient uptake and innate immunity. Higgins MK, Tkachenko O, Brown A, Reed J, Raper J, Carrington M; Proc Natl Acad Sci U S A. 2013;110:1905-1910. PMID:23319650

2: Structural basis for trypanosomal haem acquisition and susceptibility to the host innate immune system. Stodkilde K, Torvund-Jensen M, Moestrup SK, Andersen CB; Nat Commun. 2014;5:5487. PMID:25410714

3: Structural basis for ligand and innate immunity factor uptake by the trypanosome haptoglobin-haemoglobin receptor. Lane-Serff H, MacGregor P, Lowe ED, Carrington M, Higgins MK; Elife. 2014;3:e05553. PMID:25497229

4: Evolutionary diversification of the trypanosome haptoglobin-haemoglobin receptor from an ancestral haemoglobin receptor. Lane-Serff H, MacGregor P, Peacock L, Macleod OJ, Kay C, Gibson W, Higgins MK, Carrington M; Elife. 2016; [Epub ahead of print] PMID:27083048