Heme utilization by nontypeable Haemophilus influenzae is essential and dependent on Sap transporter function

J Bacteriol. 2011 May;193(10):2527-35. doi: 10.1128/JB.01313-10. Epub 2011 Mar 25.

Abstract

Bacterial strategies of innate immune evasion and essential metabolic functions are critical for commensal-host homeostasis. Previously, we showed that Sap translocator function is necessary for nontypeable Haemophilus influenzae (NTHI) behaviors that mediate diseases of the human airway. Antimicrobial peptide (AP) lethality is limited by binding mediated by the Sap complex. SapA shares homology with the dipeptide-binding protein (DppA) and the heme-binding lipoprotein (HbpA), both of which have previously been shown to bind the iron-containing compound heme, whose acquisition is essential for Haemophilus survival. Computational modeling revealed conserved SapA residues, similarly modeled to mediate heme binding in HbpA. Here, we directly demonstrate that SapA bound heme and was essential for heme utilization by iron-starved NTHI. Further, the Sap translocator permease mediated heme transport into the bacterial cytoplasm, thus defining a heretofore unknown mechanism of intracytoplasmic membrane heme transport in Haemophilus. Since we demonstrate multiple ligand specificity for the SapA-binding protein, we tested whether APs would compete with heme for SapA binding. We showed that human β-defensins 2 and 3, human cathelicidin LL-37, human neutrophil protein 1, and melittin displaced heme bound to SapA, thus supporting a hierarchy wherein immune evasion supercedes even the needed iron acquisition functions of the Sap system.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Antimicrobial Cationic Peptides / metabolism
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism*
  • Cathelicidins
  • Haemophilus influenzae / metabolism*
  • Haemophilus influenzae / pathogenicity*
  • Heme / metabolism*
  • Humans
  • Melitten / metabolism
  • Membrane Transport Proteins / chemistry
  • Membrane Transport Proteins / metabolism*
  • Models, Molecular
  • Protein Binding
  • Virulence Factors / chemistry
  • Virulence Factors / metabolism*
  • alpha-Defensins / metabolism
  • beta-Defensins / metabolism

Substances

  • Antimicrobial Cationic Peptides
  • Bacterial Proteins
  • DEFB103A protein, human
  • DEFB4A protein, human
  • Membrane Transport Proteins
  • Virulence Factors
  • alpha-Defensins
  • beta-Defensins
  • human neutrophil peptide 1
  • Melitten
  • Heme
  • Cathelicidins