Structural rearrangement of Neisseria meningitidis transferrin binding protein A (TbpA) prior to human transferrin protein (hTf) binding

Neisseria meningitidis utilization of human serum transferrin (hTF)-bound iron is an important pathogenicity determinant. The efficiency of this system would clearly be increased through preferential binding of diferric hTF over the iron-free form. To characterize this process, functionally active meningococcal transferrin-binding protein A (TbpA) and TbpB have been purified from N. meningitidis using a novel purification procedure. The association of isolated Tbps and Tbps in the presence of hTF was investigated by gel filtration. Co-purified TbpA+B formed a complex of molecular mass 300 kDa which bound 1–2 molecules of hTF. Purified TbpA formed a complex of 200 kDa, indicating association as a dimer, whereas TbpB aggregated to form multimers of variable sizes. On recombining TbpA and TbpB, a stable complex of equivalent size to co-purified TbpA+B was formed. This complex may be composed of a single TbpA dimer and 1 molecule of TbpB. The technique of surface plasmon resonance (SPR) was used to demonstrate clearly that TbpB of either high (85 kDa) or low (68 kDa) molecular-mass preferentially bound diferric hTF in comparison with iron-free hTF. This selectivity was not observed with TbpA, but was found at low levels with co-purified TbpA+B. Individual TbpA and TbpB, recombined in a 1:1 molecular ratio, showed iron-mediated discriminatory binding at an intermediate level. SPR was also used to show that TbpA and TbpB bound to distinct regions of hTF, and that prior saturation with TbpB reduced subsequent TbpA binding. The results demonstrated that hTF bound more TbpA than TbpB, with an approximate ratio of 2:1. We have demonstrated that in vitro, TbpA+B exists as a receptor complex composed of a TbpA dimer and one molecule of TbpB, and that TbpB selectively binds diferric hTF. We propose that, in vivo, TbpA and TbpB also exist as a receptor complex, with TbpB selectively binding diferric hTF, bringing it close to TbpA, the transmembrane component, where the ferric iron can be transported to the periplasm.

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Immunogenicity and antigenic heterogeneity of a human transferrin-binding protein in Neisseria meningitidis.

Infection and Immunity ◽

10.1128/iai.60.7.2887-2892.1992 ◽

1992 ◽

Vol 60 (7) ◽

pp. 2887-2892 ◽

Cited By ~ 21

Author(s):

L Ferron ◽

C M Ferreiros ◽

M T Criado ◽

M Pintor

Keyword(s):

Neisseria Meningitidis ◽

Binding Protein ◽

Human Transferrin ◽

Antigenic Heterogeneity

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The Role of the Moraxella catarrhalis CopB Protein in Facilitating Iron Acquisition From Human Transferrin and Lactoferrin

Frontiers in Microbiology ◽

10.3389/fmicb.2021.714815 ◽

2021 ◽

Vol 12 ◽

Author(s):

Clement Chan ◽

Dixon Ng ◽

Anthony B. Schryvers

Keyword(s):

Outer Membrane ◽

Indirect Effect ◽

Moraxella Catarrhalis ◽

Respiratory Infections ◽

Binding Protein ◽

Protein A ◽

Upper Respiratory Tract ◽

Human Transferrin ◽

Upper Respiratory ◽

The Impact

Moraxella catarrhalis is a Gram-negative bacterium that is responsible for a substantial proportion of upper respiratory infections in children and lower respiratory infections in the elderly. Moraxella catarrhalis resides exclusively on the mucosal surfaces of the upper respiratory tract of humans and is capable of directly acquiring iron for growth from the host glycoproteins human transferrin (hTf) and human lactoferrin (hLf). The iron-bound form of these glycoproteins is initially captured by the surface lipoproteins Tf or Lf binding protein B (TbpB or LbpB) and delivered to the integral outer membrane TonB-dependent transport (TBDT) proteins, Tf binding protein A (TbpA) or Lf binding protein A (LbpA). The extraction of iron involves conformational changes in Lf and Tf to facilitate iron removal followed by its transport across the outer membrane by a well characterized process for TBDTs. Surprisingly the disruption of the gene encoding another TBDT, CopB, results in a reduction in the ability to grow on human Tf or Lf. The possibility that this could have been due to an artifact of mutant construction that resulted in the inhibition of TonB-mediated process was eliminated by a complete deletion of the CopB gene. A systematic evaluation of the impact on growth under various conditions by deletions of the genes encoding TbpA, LbpA, and CopB as well as mutations of the iron liganding residues and TonB box region of CopB was implemented. The results indicate that although CopB is capable of effectively acquiring iron from the growth medium, it does not directly acquire iron from Tf or Lf. We propose that the indirect effect on iron transport from Tf and Lf by CopB could possibly be explained by the association of TBDTs at gaps in the peptidoglycan layer that may enhance the efficiency of the process. This concept is supported by previous studies demonstrating an indirect effect on growth of Tf and Lf by deletion of the peptidoglycan binding outer membrane lipoprotein RmpM in Neisseria that also reduced the formation of larger complexes of TBDTs.

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Binding of Human Platelet Glycoprotein lb and Actin to Fragments of Actin-Binding Protein

Thrombosis and Haemostasis ◽

10.1055/s-0038-1648421 ◽

1992 ◽

Vol 67 (02) ◽

pp. 252-257 ◽

Cited By ~ 9

Author(s):

Anne M Aakhus ◽

J Michael Wilkinson ◽

Nils Olav Solum

Keyword(s):

Actin Filaments ◽

High Speed ◽

Binding Protein ◽

Protein A ◽

Actin Binding ◽

Platelet Glycoprotein ◽

Actin Binding Protein ◽

Crossed Immunoelectrophoresis ◽

Triton X ◽

Calpain Inhibitors

SummaryActin-binding protein (ABP) is degraded into fragments of 190 and 90 kDa by calpain. A monoclonal antibody (MAb TI10) against the 90 kDa fragment of ABP coprecipitated with the glycoprotein lb (GP lb) peak observed on crossed immunoelectrophoresis of Triton X-100 extracts of platelets prepared without calpain inhibitors. MAb PM6/317 against the 190 kDa fragment was not coprecipitated with the GP lb peak under such conditions. The 90 kDa fragment was adsorbed on protein A agarose from extracts that had been preincubated with antibodies to GP lb. This supports the idea that the GP Ib-ABP interaction resides in the 90 kDa region of ABP. GP lb was sedimented with the Triton-insoluble actin filaments in trace amounts only, and only after high speed centrifugation (100,000 × g, 3 h). Both the 190 kDa and the 90 kDa fragments of ABP were sedimented with the Triton-insoluble actin filaments.

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