Stewart T J, Smith A L, Havercroft J C
Department of Pathology, University of Cambridge.
Parasitology. 1992 Dec;105 ( Pt 3):399-408. doi: 10.1017/s0031182000074576.
The complete sequence of the cDNA encoding a 20 kDa calcium-binding protein of Schistosoma mansoni (Sm20) has been determined. The predicted amino acid sequence contains 4 EF hand domains but examination of the predicted secondary structure of Sm20, together with the specific residues in each calcium-binding domain, suggests that only 1 EF hand (domain IV) is functional. Sm20 is most homologous to calmodulin, troponin C and the regulatory light-chain of myosin, particularly those of invertebrates. However, troponin C and the regulatory light-chain of myosin can be distinguished from Sm20 by size and by their differential levels of expression during the life-cycle. Sm20 also appears to be distinct from calmodulin but may be functionally equivalent to the soluble sarcoplasmic calcium-binding proteins of molluscs and crustacea which may act as a reservoir for calcium in muscle. Sm20 is encoded by a small multi-gene family whose members are clustered within a 15 kb region of the genome. A 20 kDa antigen, cross-reactive with Sm20, is expressed in Schistosoma haematobium, Fasciola hepatica and Paragonomus mexicanus.
已确定编码曼氏血吸虫20 kDa钙结合蛋白（Sm20）的cDNA的完整序列。预测的氨基酸序列包含4个EF手结构域，但对Sm20预测的二级结构以及每个钙结合结构域中的特定残基进行分析后表明，只有1个EF手（结构域IV）具有功能。Sm20与钙调蛋白、肌钙蛋白C和肌球蛋白调节轻链最为同源，尤其是无脊椎动物的这些蛋白。然而，肌钙蛋白C和肌球蛋白调节轻链在大小以及生命周期中的表达水平差异方面可与Sm20区分开来。Sm20似乎也与钙调蛋白不同，但在功能上可能等同于软体动物和甲壳类动物的可溶性肌浆钙结合蛋白，后者可能在肌肉中作为钙的储存库。Sm20由一个小的多基因家族编码，其成员聚集在基因组的一个15 kb区域内。一种与Sm20交叉反应的20 kDa抗原在埃及血吸虫、肝片吸虫和墨西哥并殖吸虫中表达。
