Knowles D P, Kappmeyer L S, Perryman L E
Agricultural Research Service, US Department of Agriculture, Pullman, WA 99164-7030, USA.
Mol Biochem Parasitol. 1997 Dec 1;90(1):69-79. doi: 10.1016/s0166-6851(97)00150-3.
Erythrocyte-stage Babesia equi expresses a 34-kDa immunodominant antigen recognized by antibody from persistently infected horses worldwide. This erythrocyte-stage surface protein, equi merozoite antigen-1 (EMA-1) is encoded by a single copy gene, and was previously shown to share 33% amino acid identity with similar sized proteins of Theileria sergenti and T. buffeli. A mean homology of 31% amino acid identity extends to similar sized proteins of T. parva, T. annulata and T. mutans. Genomic and cDNA copies of a second B. equi gene, ema2 were cloned. The single copy ema2 gene encodes a 30-kDa protein (EMA-2) that shares 52% amino acid identity with EMA-1. EMA-2 also shares a mean amino acid identity of 31% with proteins of similar molecular mass from Theileria species. EMA-1 and EMA-2 each contain a glycosylphosphatidylinositol anchor. These unique erythrocyte-stage surface proteins of B. equi and Theileria species lack antigenic repeats, and excluding the signal peptide, contain one or no cysteines. Consistent with the hypothesis that this family of proteins interacts with the erythrocyte surface, the T. species proteins possess a basic isoelectric point. The B. equi proteins have acidic isoelectric points, but 24-mer peptides within them have strongly basic net charges.
马巴贝斯虫红细胞阶段表达一种34 kDa的免疫显性抗原，该抗原可被来自世界各地持续感染马匹的抗体识别。这种红细胞阶段表面蛋白，即马裂殖子抗原-1（EMA-1）由单拷贝基因编码，先前已证明它与瑟氏泰勒虫和水牛泰勒虫大小相似的蛋白具有33%的氨基酸同一性。平均31%的氨基酸同一性同源性延伸至小泰勒虫、环形泰勒虫和变形泰勒虫大小相似的蛋白。克隆了马巴贝斯虫第二个基因ema2的基因组和cDNA拷贝。单拷贝的ema2基因编码一种30 kDa的蛋白（EMA-2），它与EMA-1具有52%的氨基酸同一性。EMA-2与泰勒虫属相似分子量的蛋白也具有平均31%的氨基酸同一性。EMA-1和EMA-2均含有糖基磷脂酰肌醇锚定。马巴贝斯虫和泰勒虫属这些独特的红细胞阶段表面蛋白缺乏抗原重复序列，除信号肽外，含有一个或没有半胱氨酸。与该蛋白家族与红细胞表面相互作用的假设一致，泰勒虫属的蛋白具有碱性等电点。马巴贝斯虫的蛋白具有酸性等电点，但其中的24肽具有强碱性净电荷。
