This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Stokes, R. H. Articles by Evans, R. W. Search for Related Content PubMed PubMed Citation Articles by Stokes, R. H. Articles by Evans, R. W.

Meningococcal Transferrin-Binding Proteins A and B Show Cooperation in Their Binding Kinetics for Human Transferrin

Metalloprotein Research Group, Randall Division of Cell and Molecular Biophysics, GKT School of Biomedical Sciences, King's College London, London,¹ Health Protection Agency, Porton Down, Salisbury, United Kingdom²

Received 14 June 2004/ Returned for modification 22 July 2004/ Accepted 24 September 2004

Neisseria meningitidis, a causative agent of bacterial meningitis and septicemia, obtains transferrin-bound iron by expressing two outer membrane-located transferrin-binding proteins, TbpA and TbpB. A novel system was developed to investigate the interaction between Tbps and human transferrin. Copurified TbpA-TbpB, recombined TbpA-TbpB, and individual TbpA and TbpB were reconstituted into liposomes and fused onto an HPA chip (BIAcore). All preparations formed stable monolayers, which, with the exception of TbpB, could be regenerated by removing bound transferrin. The ligand binding properties of these monolayers were characterized with surface plasmon resonance and shown to be specific for human transferrin. Kinetic data for diferric human transferrin binding showed that recombined TbpA-TbpB had K_a and K_d values similar to those of copurified TbpA-TbpB. Individual TbpA and TbpB also displayed K_a values similar to those of copurified TbpA-TbpB, but their K_d values were one order of magnitude higher. Chemical cross-linking studies revealed that TbpA and TbpB, in the absence of human transferrin, formed large complexes with TbpA as the predominant species. Upon human transferrin binding, a complex was formed with a molecular mass corresponding to that of a TbpB-human transferrin heterodimer as well as a higher-molecular-mass complex of this heterodimer cross-linked to TbpA. This indicates that TbpA and TbpB form a functional meningococcal receptor complex in which there is cooperativity in the human transferrin binding kinetics. However, iron loss from the diferric human transferrin-TbpA-TbpB complex was not greater than that from human transferrin alone, suggesting that additional meningococcal transport components are involved in the process of iron removal.

Editor: J. N. Weiser

This article has been cited by other articles:

• Noto, J. M., Cornelissen, C. N. (2008). Identification of TbpA Residues Required for Transferrin-Iron Utilization by Neisseria gonorrhoeae. Infect. Immun. 76: 1960-1969 [Abstract] [Full Text]