title: Point mutations in HpuB enable gonococcal HpuA deletion mutants to grow on hemoglobin.
abstract: Neisseria gonorrhoeae ordinarily requires both HpuA and HpuB to use hemoglobin (Hb) as a source of iron for growth. Deletion of HpuA resulted in reduced Hb binding and failure of growth on Hb. We identified rare Hb-utilizing colonies (Hb(+)) from an hpuA deletion mutant of FA1090, which fell into two phenotypic classes. One class of the Hb(+) revertants required expression of both TonB and HpuB for growth on Hb, while the other class required neither TonB nor HpuB. All TonB/HpuB-dependent mutants had single amino acid alterations in HpuB, which occurred in clusters, particularly near the C terminus. The point mutations in HpuB did not restore normal Hb binding. Human serum albumin inhibited Hb-dependent growth of HpuB point mutants lacking HpuA but did not inhibit growth when expression of HpuA was restored. Thus, HpuB point mutants internalized heme in the absence of HpuA despite reduced binding of Hb. HpuA facilitated Hb binding and was important in allowing use of heme from Hb for growth.
authors.affiliation: Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: Ching-Ju
authors.initials: CJ
authors.lastname: Chen
authors.forename: Dalton
authors.initials: D
authors.lastname: Mclean
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Thomas
authors.forename: James E
authors.initials: JE
authors.lastname: Anderson
authors.forename: P Frederick
authors.initials: PF
authors.lastname: Sparling
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics; D006418:Heme / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009344:Neisseria gonorrhoeae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D017354:Point Mutation; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D006454:Hemoglobins; C094109:HmbR protein, Neisseria meningitidis; C445303:HpuA protein, Neisseria; C105625:HpuB protein, Neisseria; D011956:Receptors, Cell Surface; D006418:Heme