McBride Jere W, Doyle C Kuyler, Zhang Xiaofeng, Cardenas Ana Maria, Popov Vsevolod L, Nethery Kimberly A, Woods Michael E
Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555, USA.
Infect Immun. 2007 Jan;75(1):74-82. doi: 10.1128/IAI.01494-06. Epub 2006 Nov 6.
Ehrlichia canis has a small subset of major immunoreactive proteins that includes a 19-kDa protein that elicits an early Ehrlichia-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 the Ehrlichia chaffeensis variable-length PCR target (VLPT) protein. E. canis gp19 has substantial carboxyl-terminal amino acid homology (59%) with E. chaffeensis VLPT and the same chromosomal location; however, the E. chaffeensis VLPT gene (594 bp) has tandem repeats that are not present in the E. canis gp19 gene (414 bp). Consistent with other ehrlichial glycoproteins, the gp19 protein exhibited a larger-than-predicted mass (approximately 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 an E. 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.
犬埃立克体有一小部分主要免疫反应蛋白，其中包括一种19 kDa的蛋白，该蛋白能在感染犬体内引发早期埃立克体特异性抗体反应。我们在此报告犬埃立克体恰菲埃立克体可变长度PCR靶标（VLPT）蛋白高度保守的19 kDa主要免疫反应糖蛋白（gp19）直系同源物的鉴定及分子特征。犬埃立克体gp19与恰菲埃立克体VLPT在羧基末端氨基酸上有大量同源性（59%）且位于相同染色体位置；然而，恰菲埃立克体VLPT基因（594 bp）有串联重复序列，而犬埃立克体gp19基因（414 bp）中不存在。与其他埃立克体糖蛋白一致，gp19蛋白表现出比预测更大的质量（约3 kDa），在富含氨基末端丝氨酸/苏氨酸/谷氨酸（STE）的区域（26个氨基酸）预测有O-连接糖基化位点，在重组gp19蛋白上检测到碳水化合物，在重组氨基末端多肽上检测到中性糖葡萄糖和半乳糖。犬埃立克体gp19的组成由五种主要氨基酸组成，即半胱氨酸、谷氨酸、酪氨酸、丝氨酸和苏氨酸，集中在富含STE的区域以及以半胱氨酸和酪氨酸为主（55%）的羧基末端结构域。氨基末端富含STE的区域包含一个主要的种特异性抗体表位，能被来自犬埃立克体感染犬的血清强烈识别。重组糖肽表位与抗体的反应性比合成（非糖基化）肽强得多，高碘酸盐处理重组糖肽表位会降低其免疫反应性，证明了碳水化合物免疫决定簇的重要性。gp19蛋白存在于网状细胞和致密核心细胞上，在细胞外的纤维状基质中被发现，并与桑葚体膜、宿主细胞质和细胞核相关。
