Kamchonwongpaisan S, Samoff E, Meshnick S R
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor 48109-2029, USA.
Mol Biochem Parasitol. 1997 Jun;86(2):179-86. doi: 10.1016/s0166-6851(97)02855-7.
Malaria parasites break down human hemoglobin to its constituent amino acids by cysteine and aspartic proteinases. However, no one has previously been able to identify hemoglobin cleavage products in intact parasites. When isolated parasites were subjected to non-denaturing polyacrylamide gels electrophoresis, a unique protein band was found which contains heme and reacts with anti-human hemoglobin antibodies. This protein does not appear to represent oxidized or glycosylated hemoglobin, and is present in isolated parasites but not in the cytosol of infected or uninfected erythrocytes. When this band was eluted and subjected to SDS polyacrylamide gel electrophoresis, three bands were seen on Western blots. The proteins in these bands contain proteins with the N-terminal sequences of alpha- and beta-globin chains but molecular masses of only 13.2-13.4 kDa. These data suggest that hemoglobin alpha- and beta-chains are initially cleaved within the parasite phagolysosome to release peptides of 15-17 and 23-25 amino acids from the C-termini of alpha- and beta-globin chains, respectively. Production of the hemoglobin breakdown products was inhibited by E-64, a cysteine proteinase inhibitor, suggesting the involvement of a cysteine proteinase in an early step of hemoglobin degradation.
疟原虫通过半胱氨酸和天冬氨酸蛋白酶将人血红蛋白分解为其组成氨基酸。然而，此前没有人能够在完整的疟原虫中鉴定出血红蛋白裂解产物。当将分离的疟原虫进行非变性聚丙烯酰胺凝胶电泳时，发现了一条独特的蛋白带，该蛋白带含有血红素并能与抗人血红蛋白抗体发生反应。这种蛋白似乎不代表氧化或糖基化的血红蛋白，它存在于分离的疟原虫中，但不存在于感染或未感染红细胞的胞质溶胶中。当洗脱这条带并进行SDS聚丙烯酰胺凝胶电泳时，在Western印迹上可见三条带。这些带中的蛋白质含有具有α-和β-珠蛋白链N端序列的蛋白质，但分子量仅为13.2 - 13.4 kDa。这些数据表明，血红蛋白α链和β链最初在疟原虫吞噬溶酶体内被切割，分别从α链和β链的C端释放出15 - 17个和23 - 25个氨基酸的肽段。半胱氨酸蛋白酶抑制剂E - 64抑制了血红蛋白分解产物的产生，这表明半胱氨酸蛋白酶参与了血红蛋白降解的早期步骤。
