Abstract
The haptoglobin-haemoglobin receptor of the African trypanosome species, Trypanosoma brucei, is expressed when the parasite is in the bloodstream of the mammalian host, allowing it to acquire haem through the uptake of haptoglobin-haemoglobin complexes. Here we show that in Trypanosoma congolense this receptor is instead expressed in the epimastigote developmental stage that occurs in the tsetse fly, where it acts as a haemoglobin receptor. We also present the structure of the T. congolense receptor in complex with haemoglobin. This allows us to propose an evolutionary history for this receptor, charting the structural and cellular changes that took place as it adapted from a role in the insect to a new role in the mammalian host.
Highlights
Infection of livestock by African trypanosomes has a significant effect on food production in subSaharan Africa (Shaw et al, 2004)
The complex that it forms with the receptor is not sufficiently strong to remain intact during gel filtration chromatography and haptoglobin-haemoglobin complexes (HpHb) and the receptor elute in separate peaks, confirming that the receptor has a low affinity for HpHb
It was a reasonable expectation that orthologues in other African trypanosome species, such as T. congolense and T. vivax, would have a similar function
Summary
Infection of livestock by African trypanosomes has a significant effect on food production in subSaharan Africa (Shaw et al, 2004). T. brucei epimastigotes attach to the epithelium in the salivary glands away from the digestive tract, whereas T. congolense and T. vivax attach in the proboscis within the digestive tract (Hoare, 1972; Peacock et al, 2012; Jefferies et al, 1987). The basis for these different tissue tropisms is not known.
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