Open AccessCharacterization of a Novel Outer Membrane Hemin-Binding Protein of Porphyromonas gingivalis
Author(s) -
Stuart G. Dashper,
A. Hendtlass,
Nada Slakeski,
Christine A. Jackson,
Keith J. Cross,
Lynette Brownfield,
Robert W. Hamilton,
Ian Barr,
Eric C. Reynolds
Publication year - 2000
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.182.22.6456-6462.2000
Subject(s) - hemin , porphyromonas gingivalis , biology , bacterial outer membrane , heme , peptide sequence , biochemistry , microbiology and biotechnology , escherichia coli , bacteria , gene , genetics , enzyme
Porphyromonas gingivalis is a gram-negative, anaerobic coccobacillus that has been implicated as a major etiological agent in the development of chronic periodontitis. In this paper, we report the characterization of a protein, IhtB (iron heme transport; formerly designated Pga30), that is an outer membrane hemin-binding protein potentially involved in iron assimilation byP. gingivalis . IhtB was localized to the cell surface ofP. gingivalis by Western blot analysis of a Sarkosyl-insoluble outer membrane preparation and by immunocytochemical staining of whole cells using IhtB peptide-specific antisera. The protein, released from the cell surface, was shown to bind to hemin using hemin-agarose. The growth of heme-limited, but not heme-replete,P. gingivalis cells was inhibited by preincubation with IhtB peptide-specific antisera. TheihtB gene was located between an open reading frame encoding a putative TonB-linked outer membrane receptor and three open reading frames that have sequence similarity to ATP binding cassette transport system operons in other bacteria. Analysis of the deduced amino acid sequence of IhtB showed significant similarity to theSalmonella typhimurium protein CbiK, a cobalt chelatase that is structurally related to the ATP-independent family of ferrochelatases. Molecular modeling indicated that the IhtB amino acid sequence could be threaded onto the CbiK fold with the IhtB structural model containing the active-site residues critical for chelatase activity. These results suggest that IhtB is a peripheral outer membrane chelatase that may remove iron from heme prior to uptake byP. gingivalis .