The lab’s first set of questions centre on the interactions with the mammalian host and in particular the molecular and cellular mechanisms through which the trypanosome is able to utilise receptors to endocytose large proteins from the host without being susceptible to an immunoglobulin mediated response.
This has led to discoveries of how the. T. brucei haptoglobin-haemoglobin receptor (HpHbR) evolved from an insect-stage haemoglobin receptor and how it works in the context of the variant surfaceglycoprotein coat. The structure of the transferrin receptor has been determined and indicates that heterogeneity in the gene family is related to long term antigenic avoidance. We have also discovered two receptors of complement components, characterising the factor H receptor in molecular detail andshown it is involved in successful infection of tsetses. Deletion of the C3 receptor leads to attenuation ofinfection and is undergoing structural analysis.
HpHbR is central to human infectivity. Most African trypanosomes, such as T. brucei brucei and T.congolense, cannot infect humans due to innate immunity. For T. brucei brucei, this is mediated bytrypanolytic factors 1 and 2 (TLF1 and TLF2). TLFs are characterised by the presence of apolipoproteinL1 (ApoL1) and haptoglobin-related protein (Hpr). In TLF1, Hpr is complexed with hemoglobin (HprHb)and the trypanosome HpHbR is exploited for uptake via binding of the HprHb component to thereceptor. After endocytosis of TLF1, ApoL1 is trafficked to the lysosome where it causes swellingresulting in cell death.
HpHbR is central to human infectivity. Most African trypanosomes, such as T. brucei brucei and T.congolense, cannot infect humans due to innate immunity. For T. brucei brucei, this is mediated bytrypanolytic factors 1 and 2 (TLF1 and TLF2). TLFs are characterised by the presence of apolipoproteinL1 (ApoL1) and haptoglobin-related protein (Hpr). In TLF1, Hpr is complexed with hemoglobin (HprHb)and the trypanosome HpHbR is exploited for uptake via binding of the HprHb component to thereceptor. After endocytosis of TLF1, ApoL1 is trafficked to the lysosome where it causes swellingresulting in cell death.
In T. b. rhodesiese the expression of SRA is sufficient to confer resistance to human serum. SRA is also related to VSGs but contains a large internal deletion of ~120 amino acids. We have modelled the structure of SRA using the VSG N-terminal domain structure. This has been highly successful in suggesting future experimental approaches, below is a comparison of models of a VSG and SRA. We are currently aiming to solve the structure of SRA binding its ligand human apolipoprotein L-Iafter showing previous models were incorrect.
Live images of cells expressing p67-mChFP to mark the lysosome and showing the effect ofafter 60 mins in bovine or human serum. p67 is a type 1 membrane protein localised to thelysosome and the mChFP tag is on the cytoplasmic face of the lysosomal membrane.
Mapping of the ApoL1 binding site of SRA byhydrogen-deuterium exchange massspectrometry. Exchange differences mappedon the structure of SRA in two views identify thelocations P of protected peptides.
