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PDBsum entry 4x0l
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Oxygen transport
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PDB id
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4x0l
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Contents |
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141 a.a.
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144 a.a.
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259 a.a.
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References listed in PDB file
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Key reference
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Title
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Structural basis for ligand and innate immunity factor uptake by the trypanosome haptoglobin-Haemoglobin receptor.
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Authors
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H.Lane-Serff,
P.Macgregor,
E.D.Lowe,
M.Carrington,
M.K.Higgins.
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Ref.
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Elife, 2014,
3,
e05553.
[DOI no: ]
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PubMed id
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Abstract
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The haptoglobin-haemoglobin receptor (HpHbR) of African trypanosomes allows
acquisition of haem and provides an uptake route for trypanolytic factor-1, a
mediator of innate immunity against trypanosome infection. In this study, we
report the structure of Trypanosoma brucei HpHbR in complex with human
haptoglobin-haemoglobin (HpHb), revealing an elongated ligand-binding site that
extends along its membrane distal half. This contacts haptoglobin and the
β-subunit of haemoglobin, showing how the receptor selectively binds HpHb over
individual components. Lateral mobility of the
glycosylphosphatidylinositol-anchored HpHbR, and a ∼50° kink in the receptor,
allows two receptors to simultaneously bind one HpHb dimer. Indeed, trypanosomes
take up dimeric HpHb at significantly lower concentrations than monomeric HpHb,
due to increased ligand avidity that comes from bivalent binding. The structure
therefore reveals the molecular basis for ligand and innate immunity factor
uptake by trypanosomes and identifies adaptations that allow efficient ligand
uptake in the context of the complex trypanosome cell surface.
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