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J. Bacteriol., 10 1997, 6400-6407, Vol 179, No. 20
G Renaud-Mongenie, D Poncet, L von Olleschik-Elbheim, T Cournez, M Mignon, MA Schmidt and MJ Quentin-Millet
Transferrin-binding protein B (TbpB) from Neisseria meningitidis binds
human transferrin (hTf) at the surface of the bacterial cell as part of the
iron uptake process. To identify hTf binding sites within the meningococcal
TbpB, defined regions of the molecule were produced in Escherichia coli by
a translational fusion expression system and the ability of the recombinant
proteins (rTbpB) to bind peroxidase- conjugated hTf was characterized by
Western blot and dot blot assays. Both the N-terminal domain (amino acids
[aa] 2 to 351) and the C- terminal domain (aa 352 to 691) were able to bind
hTf, and by a peptide spot synthesis approach, two and five hTf binding
sites were identified in the N- and C-terminal domains, respectively. The
hTf binding activity of three rTbpB deletion variants constructed within
the central region (aa 346 to 543) highlighted the importance of a specific
peptide (aa 377 to 394) in the ligand interaction. Taken together, the
results indicated that the N- and C-terminal domains bound hTf
approximately 10 and 1000 times less, respectively, than the full- length
rTbpB (aa 2 to 691), while the central region (aa 346 to 543) had a binding
avidity in the same order of magnitude as the C-terminal domain. In
contrast with the hTf binding in the N-terminal domain, which was mediated
by conformational epitopes, linear determinants seemed to be involved in
the hTf binding in the C-terminal domain. The host specificity for
transferrin appeared to be mediated by the N- terminal domain of the
meningococcal rTbpB rather than the C-terminal domain, since we report that
murine Tf binds to the C-terminal domain. Antisera raised to both N- and
C-terminal domains were bactericidal for the parent strain, indicating that
both domains are accessible at the bacterial surface. We have thus
identified hTf binding sites within each domain of the TbpB from N.
meningitidis and propose that the N- and C-terminal domains together
contribute to the efficient binding of TbpB to hTf with their respective
affinities and specificities for determinants of their ligand.
Copyright © 1997, American Society for Microbiology
Identification of human transferrin-binding sites within meningococcal transferrin-binding protein B
Pasteur Merieux Connaught, Marcy l'Etoile, France.
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