title: Differential binding of apo and holo human transferrin to meningococci and co-localisation of the transferrin-binding proteins (TbpA and TbpB).
abstract: Apo-transferrin (apo-hTf) and holo-transferrin (holo-hTf) were separately conjugated to 15-nm colloidal gold. Iron-restricted Neisseria meningitidis strain SD (B:15:P1.16) bound up to three-fold more holo-hTf than apo-hTf (p <0.001). The ability of meningococcal mutants lacking either transferrin-binding protein A (TbpA) or TbpB to discriminate between apo-hTf and holo-hTf was also investigated. There was no significant difference between the amount of gold-labelled apo-transferrin bound by the isogenic TbpA mutant (expressing TbpB) and the parent strain, whereas an isogenic TbpB mutant (expressing TbpA) bound significantly less gold-labelled apo-hTf. The isogenic TbpA and TbpB mutants and the parent strain all bound significantly more holo-hTf than apo-hTf, whereas the double 'knock-out' mutant failed to bind hTf irrespective of the iron-loading. In the isogenic mutants, TbpB was more effective in binding either apo- or holo-hTf than TbpA. Monoclonal antibodies against TbpA and TbpB were used to co-localise the transferrin-binding proteins on strain SD. The ratio of TbpA:TbpB was approximately 1:1. TbpA and TbpB were occasionally observed in close proximity to each other, but the two proteins were generally quite separate, which may indicate that they do not usually form a complex to act as a transferrin receptor.
authors.affiliation: Microbial Pathogenicity Research Group, Institute of Infections and Immunity, Queen's Medical Centre, Nottingham.
authors.forename: N B
authors.initials: NB
authors.lastname: Powell
authors.forename: K
authors.initials: K
authors.lastname: Bishop
authors.forename: H M
authors.initials: HM
authors.lastname: Palmer
authors.forename: D A
authors.initials: DA
authors.lastname: Ala'Aldeen
authors.forename: A R
authors.initials: AR
authors.lastname: Gorringe
authors.forename: S P
authors.initials: SP
authors.lastname: Borriello
mesh_terms: D000911:Antibodies, Monoclonal; D001059:Apoproteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D033862:Iron-Binding Proteins; D009154:Mutation; D009345:Neisseria meningitidis / Q000235:genetics / Q000502:physiology*; D011990:Receptors, Transferrin / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*; D033863:Transferrin-Binding Proteins
chemical_list: D000911:Antibodies, Monoclonal; D001059:Apoproteins; D002352:Carrier Proteins; D033862:Iron-Binding Proteins; D011990:Receptors, Transferrin; D014168:Transferrin; D033863:Transferrin-Binding Proteins; C028284:apotransferrin; C110714:holotransferrin