An immunoreactive 38-kilodalton protein of Ehrlichia canis shares structural homology and iron-binding capacity with the ferric ion-binding protein family

C. Kuyler Doyle, Xiaofeng Zhang, Vsevolod Popov, Jere McBride

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Abstract

Ehrlichiae are tick-transmitted, gram-negative, obligately intracellular bacteria that live and replicate in cytoplasmic vacuoles, but little is known about iron acquisition mechanisms necessary for their survival. In this study, a genus-conserved immunoreactive ferric ion-binding protein (Fbp) of Ehrlichia canis was identified and its iron-binding capability was investigated. E. canis Fbp was homologous to a family of periplasmic Fbp's involved in iron acquisition and transport in gram-negative bacteria. E. canis Fbp had a molecular mass (38 kDa) consistent with those of Fbp's in other bacteria and exhibited substantial immunoreactivity in its native conformation. The predicted three-dimensional structure of E. canis Fbp demonstrated conservation of important Fbp family structural motifs: two domains linked with a polypeptide "hinge" region. Under iron-binding conditions, the recombinant Fbp exhibited an intense red color and an absorbance spectrum indicative of iron binding, and it bound Fe(III) but not Fe(II). Fbp was observed primarily in the cytoplasm of the reficulate forms of E. canis and Ehrlichia chaffeensis but was notably found on extracellular morula fibers in morulae containing dense-cored organisms. Although expression of Fbp is regulated through an operon of three functionally linked genes in other gram-negative bacteria, the absence of an intact fbp operon in Ehrlichia spp. suggests that genes involved in ehrlichial iron acquisition have been subject to reductive evolution.

Original languageEnglish (US)
Pages (from-to)62-69
Number of pages8
JournalInfection and Immunity
Volume73
Issue number1
DOIs
StatePublished - Jan 2005

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Ehrlichia canis
Carrier Proteins
Iron
Ions
Proteins
Ehrlichia
Morula
Operon
Gram-Negative Bacteria
Ehrlichia chaffeensis
Bacteria
Ticks
Vacuoles
Genes
Cytoplasm
Color
Peptides

ASJC Scopus subject areas

  • Immunology

Cite this

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title = "An immunoreactive 38-kilodalton protein of Ehrlichia canis shares structural homology and iron-binding capacity with the ferric ion-binding protein family",
abstract = "Ehrlichiae are tick-transmitted, gram-negative, obligately intracellular bacteria that live and replicate in cytoplasmic vacuoles, but little is known about iron acquisition mechanisms necessary for their survival. In this study, a genus-conserved immunoreactive ferric ion-binding protein (Fbp) of Ehrlichia canis was identified and its iron-binding capability was investigated. E. canis Fbp was homologous to a family of periplasmic Fbp's involved in iron acquisition and transport in gram-negative bacteria. E. canis Fbp had a molecular mass (38 kDa) consistent with those of Fbp's in other bacteria and exhibited substantial immunoreactivity in its native conformation. The predicted three-dimensional structure of E. canis Fbp demonstrated conservation of important Fbp family structural motifs: two domains linked with a polypeptide {"}hinge{"} region. Under iron-binding conditions, the recombinant Fbp exhibited an intense red color and an absorbance spectrum indicative of iron binding, and it bound Fe(III) but not Fe(II). Fbp was observed primarily in the cytoplasm of the reficulate forms of E. canis and Ehrlichia chaffeensis but was notably found on extracellular morula fibers in morulae containing dense-cored organisms. Although expression of Fbp is regulated through an operon of three functionally linked genes in other gram-negative bacteria, the absence of an intact fbp operon in Ehrlichia spp. suggests that genes involved in ehrlichial iron acquisition have been subject to reductive evolution.",
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T1 - An immunoreactive 38-kilodalton protein of Ehrlichia canis shares structural homology and iron-binding capacity with the ferric ion-binding protein family

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AU - Zhang, Xiaofeng

AU - Popov, Vsevolod

AU - McBride, Jere

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