Open AccessIdentification of a Glycosylated Ehrlichia canis 19-Kilodalton Major Immunoreactive Protein with a Species-Specific Serine-Rich Glycopeptide Epitope
Author(s) -
Jere W. McBride,
C. Kuyler Doyle,
Xiaofeng Zhang,
Ana Marı́a Cárdenas,
Vsevolod L. Popov,
Kimberly A. Nethery,
Michael Woods
Publication year - 2007
Publication title -
infection and immunity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.508
H-Index - 220
eISSN - 1070-6313
pISSN - 0019-9567
DOI - 10.1128/iai.01494-06
Subject(s) - biology , ehrlichia canis , epitope , ehrlichia chaffeensis , microbiology and biotechnology , biochemistry , amino acid , recombinant dna , threonine , peptide sequence , glycosylation , serine , antibody , gene , polymerase chain reaction , genetics , serology , enzyme
Ehrlichia canis has a small subset of major immunoreactive proteins that includes a 19-kDa protein that elicits an earlyEhrlichia -specific antibody response in infected dogs. We report herein the identification and molecular characterization of this highly conserved 19-kDa major immunoreactive glycoprotein (gp19) ortholog of theEhrlichia chaffeensis variable-length PCR target (VLPT) protein.E. canis gp19 has substantial carboxyl-terminal amino acid homology (59%) withE. chaffeensis VLPT and the same chromosomal location; however, theE. chaffeensis VLPT gene (594 bp) has tandem repeats that are not present in theE. canis gp19 gene (414 bp). Consistent with other ehrlichial glycoproteins, the gp19 protein exhibited a larger-than-predicted mass (∼3 kDa), O-linked glycosylation sites were predicted in an amino-terminal serine/threonine/glutamate (STE)-rich patch (26 amino acids), carbohydrate was detected on the recombinant gp19 protein, and the neutral sugars glucose and galactose were detected on the recombinant amino-terminal polypeptide.E. canis gp19 composition consists of five predominant amino acids, cysteine, glutamate, tyrosine, serine, and threonine, concentrated in the STE-rich patch and a carboxyl-terminal domain predominated by cysteine and tyrosine (55%). The amino-terminal STE-rich patch contained a major species-specific antibody epitope strongly recognized by serum from anE. canis- infected dog. The recombinant glycopeptide epitope was substantially more reactive with antibody than the synthetic (nonglycosylated) peptide, and periodate treatment of the recombinant glycopeptide epitope reduced its immunoreactivity, demonstrating the importance of a carbohydrate immunodeterminant(s). The gp19 protein was present on reticulate and dense-cored cells, and it was found extracellularly in the fibrillar matrix and associated with the morula membrane, the host cell cytoplasm, and the nucleus.