PMID:21441512

Citation	Mason, KM, Raffel, FK, Ray, WC and Bakaletz, LO (2011) Heme utilization by nontypeable Haemophilus influenzae is essential and dependent on Sap transporter function. J. Bacteriol. 193:2527-35
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.
Links	PubMed PMC3133164 Online version:10.1128/JB.01313-10
Keywords	Antimicrobial Cationic Peptides/metabolism; Bacterial Proteins/chemistry; Bacterial Proteins/metabolism; 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
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
HAEI8:Q4QL73		GO:0015886: heme transport	ECO:0000315:		P		Figure 3A&B. The iron-starved parent strain was unable to grow when subcultured in heme-depleted medium, which indicated that the microorganism was sufficiently starved of all internal iron stores. Parent strain growth was restored, however, when the strain was subcultured in the presence of heme. Although the SapA-deficient strain demonstrated growth comparable to that of the parent in a heme-replete environment, following iron starvation, the cells were unable to utilize heme for growth.	complete CACAO 5998
HAEI8:Q4QL74		GO:0015886: heme transport	ECO:0000315:		P		Figure 4A. Shows that a functional sapB permease is required for normal growth of NTHI because the sapB-deficient mutant was unable to utilize heme as an iron source	complete CACAO 6000
HAEI8:Q4QL74	involved_in	GO:0015886: heme transport	ECO:0000315: mutant phenotype evidence used in manual assertion		P		Seeded From UniProt	complete
HAEI8:Q4QL75		GO:0015886: heme transport	ECO:0000315: mutant phenotype evidence used in manual assertion		P		Figure 4A. Shows that a functional sapC permease is required for normal growth of NTHI because the sapC-deficient mutant was unable to utilize heme as an iron source	complete CACAO 6001

References

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