Structural basis for trypanosomal haem acquisition and susceptibility to the host innate immune system

Nat Commun. 2014 Nov 20:5:5487. doi: 10.1038/ncomms6487.

Abstract

Sleeping sickness is caused by trypanosome parasites, which infect humans and livestock in Sub-Saharan Africa. Haem is an important growth factor for the parasites and is acquired from the host by receptor-mediated uptake of haptoglobin (Hp)-haemoglobin (Hb) complexes. The parasite Hp-Hb receptor (HpHbR) is also a target for a specialized innate immune defence executed by trypanosome-killing lipoprotein particles containing an Hp-related protein in complex with Hb. Here we report the structure of the multimeric complex between human Hp-Hb and Trypanosoma brucei brucei HpHbR. Two receptors forming kinked three-helical rods with small head regions bind to Hp and the β-subunits of Hb (βHb), with one receptor at each end of the dimeric Hp-Hb complex. The Hb β-subunit haem group directly associates with the receptors, which allows for sensing of haem-containing Hp-Hb. The HpHbR-binding region of Hp is conserved in Hp-related protein, indicating an identical recognition of Hp-Hb and trypanolytic particles by HpHbR in human plasma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Haptoglobins / metabolism*
  • Heme / metabolism*
  • Hemoglobins / metabolism*
  • Humans
  • Immunity, Innate / immunology
  • Protein Binding
  • Protein Structure, Tertiary
  • Protozoan Proteins / immunology
  • Protozoan Proteins / metabolism*
  • Receptors, Cell Surface / immunology
  • Receptors, Cell Surface / metabolism*
  • Trypanosoma brucei brucei / metabolism*

Substances

  • Haptoglobins
  • Hemoglobins
  • Protozoan Proteins
  • Receptors, Cell Surface
  • hemoglobin-haptoglobin receptor
  • Heme
  • hemoglobin B

Associated data

  • PDB/4WJG