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Clinical and Diagnostic Laboratory Immunology, May 1999, p. 392-399, Vol. 6, No. 3
Department of Pathology and WHO Collaborating
Center for Tropical Diseases, University of Texas Medical Branch,
Galveston, Texas 77555-0609
Received 24 August 1998/Returned for modification 23 November
1998/Accepted 14 January 1999
A gene encoding a 28-kDa protein of Ehrlichia canis was
cloned, sequenced, and expressed, and a comparative molecular analysis with homologous genes of E. canis, Cowdria
ruminantium, and Ehrlichia chaffeensis was performed.
The complete gene has an 834-bp open reading frame encoding a protein
of 278 amino acids with a predicted molecular mass of 30.5 kDa. An
N-terminal signal sequence was identified, suggesting that the protein
undergoes posttranslational modification to a mature 27.7-kDa protein
(P28). The E. canis p28 gene has significant nucleic acid
and amino acid sequence homologies with the E. chaffeensis
outer membrane protein-1 (omp-1) gene family, with the
Cowdria ruminantium map-1 gene, and with other E. canis 28-kDa-protein genes. Southern blotting revealed the
presence of at least two additional homologous p28 gene
copies in the E. canis genome, confirming that
p28 is a member of a polymorphic multiple-gene family.
Amino acid sequence analysis revealed that E. canis P28 has
four variable regions, and it shares similar surface-exposed regions,
antigenicity, and T-cell motifs with E. chaffeensis P28.
The p28 genes from seven different E. canis isolates were identical, indicating that the gene for this major immunoreactive protein is highly conserved. In addition, reactivity of
sera from clinical cases of canine ehrlichiosis with the recombinant P28 demonstrated that the recombinant protein may be a reliable serodiagnostic antigen.
1071-412X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Molecular Cloning of the Gene for a Conserved Major
Immunoreactive 28-Kilodalton Protein of Ehrlichia canis:
a Potential Serodiagnostic Antigen
*
Corresponding author. Mailing address: Department of
Pathology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0609. Phone: (409) 772-2856. Fax: (409) 772-2500. E-mail: dwalker{at}utmb.edu.
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