Identification of functionally important regions of a haemoglobin receptor from Neisseria meningitidis

Microbiology (Reading). 2003 Dec;149(Pt 12):3423-3435. doi: 10.1099/mic.0.26448-0.

Abstract

The HmbR outer-membrane receptor enables Neisseria meningitidis to use haemoglobin (Hb) as a source of iron. This protein functions by binding Hb, removing haem from it, and releasing the haem into the periplasm. Functionally important HmbR receptor domains were discerned using a series of HmbR deletions and site-directed mutations. Mutations exhibiting similar defective phenotypes in N. meningitidis fell into two groups. The first group of mutations affected Hb binding and were located in putative extracellular loops (L) L2 (amino acid residues (aa) 192-230) and L3 (aa 254-284). The second group of mutations resulted in a failure to utilize Hb but proficiency in Hb binding was retained. These mutations localized to the putative extracellular loops L6 (aa 420-462) and L7 (aa 486-516). A highly conserved protein motif found in all haem/Hb receptors, within putative extracellular loop L7 of HmbR, is essential for Hb utilization but not required for Hb binding. This finding suggests a mechanistic involvement of this motif in haem removal from Hb. In addition, an amino-terminal deletion in the putative cork-like domain of HmbR affected Hb usage but not Hb binding. This result supports a role of the cork domain in utilization steps that are subsequent to Hb binding.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Binding Sites / genetics
  • DNA, Bacterial / genetics
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Hemoglobins / metabolism
  • Humans
  • In Vitro Techniques
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Neisseria meningitidis / genetics
  • Neisseria meningitidis / metabolism*
  • Neisseria meningitidis / pathogenicity
  • Phenotype
  • Protein Structure, Tertiary
  • Receptors, Cell Surface / chemistry*
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Deletion

Substances

  • Bacterial Proteins
  • DNA, Bacterial
  • Hemoglobins
  • HmbR protein, Neisseria meningitidis
  • Receptors, Cell Surface
  • Recombinant Proteins