Karcz S R, Herrmann V R, Trottein F, Cowman A F
Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria, Australia.
Mol Biochem Parasitol. 1994 May;65(1):123-33. doi: 10.1016/0166-6851(94)90121-x.
The transvacuolar pH gradient determines, to a significant extent, the distribution of the antimalarial drug chloroquine in Plasmodium falciparum. A proton pump, similar to the vacuolar ATPase found in many cell types, appears to regulate a pH gradient across the membranes of acidic compartments of the parasite. In order to understand and define the components involved in the maintenance of the vacuolar pH gradient, we have cloned and characterized a gene, designated VAP B, encoding a P. falciparum homologue of the B subunit of the vacuolar ATPase. The VAP B gene encodes a protein of 494 amino acids which has between 69% and 74% amino acid identity with the sequences of vacuolar ATPase B subunits of other organisms. The VAP B gene exists as a single copy gene on chromosome 4 that gives rise to a RNA transcript of 2.4 kb. Antibodies raised to the VAP B protein react specifically with a protein of 56-kDa, consistent with the size predicted from the gene sequence and with the homologous protein from other organisms. The 56-kDa protein is expressed throughout the asexual life cycle and subcellular localization by indirect immunofluorescence shows that the protein has a heterogeneous distribution over most of the parasite. This suggests that the function of the vacuolar proton ATPase is not confined to the regulation of the pH of the digestive vacuole.
液泡间pH梯度在很大程度上决定了抗疟药物氯喹在恶性疟原虫中的分布。一种类似于许多细胞类型中发现的液泡ATP酶的质子泵，似乎在调节寄生虫酸性区室膜上的pH梯度。为了理解和确定维持液泡pH梯度所涉及的成分，我们克隆并鉴定了一个名为VAP B的基因，它编码液泡ATP酶B亚基的恶性疟原虫同源物。VAP B基因编码一个494个氨基酸的蛋白质，与其他生物体液泡ATP酶B亚基的序列具有69%至74%的氨基酸同一性。VAP B基因作为单拷贝基因存在于4号染色体上，产生一个2.4 kb的RNA转录本。针对VAP B蛋白产生的抗体与一个56 kDa的蛋白特异性反应，这与基因序列预测的大小以及来自其他生物体的同源蛋白一致。56 kDa的蛋白在整个无性生命周期中都有表达，间接免疫荧光的亚细胞定位显示该蛋白在寄生虫的大部分区域分布不均一。这表明液泡质子ATP酶的功能并不局限于调节消化液泡的pH。
