Discussion

The haptoglobin-haemoglobin receptor of Trypanosoma brucei is expressed by the bloodstage form of the parasite, allowing acquisition of haem. We show that in T. congolense, the major species responsible for causing nagana in cattle, this receptor is instead expressed in the epimastigote developmental stage that occurs in the tsetse fly, where it acts as a haemoglobin receptor. Additionally, we present the structure of the T. congolense receptor in complex with haemoglobin. We propose an evolutionary history for this receptor, identifying the changes that took place as it adapted from a role in the insect to a new role in the mammalian host. The haptoglobin-haemoglobin receptor of Trypanosoma brucei is expressed by the bloodstage form of the parasite, allowing acquisition of haem. We show that in T. congolense, the major species responsible for causing nagana in cattle, this receptor is instead expressed in the epimastigote developmental stage that occurs in the tsetse fly, where it acts as a haemoglobin receptor. Additionally, we present the structure of the T. congolense receptor in complex with haemoglobin. We propose an evolutionary history for this receptor, identifying the changes that took place as it adapted from a role in the insect to a new role in the mammalian host. The haptoglobin-haemoglobin receptor of Trypanosoma brucei is expressed by the bloodstage form of the parasite, allowing acquisition of haem. We show that in T. congolense, the major species responsible for causing nagana in cattle, this receptor is instead expressed in the epimastigote developmental stage that occurs in the tsetse fly, where it acts as a haemoglobin receptor. Additionally, we present the structure of the T. congolense receptor in complex with haemoglobin. We propose an evolutionary history for this receptor, identifying the changes that took place as it adapted from a role in the insect to a new role in the mammalian host.