Asai T, Howe D K, Nakajima K, Nozaki T, Takeuchi T, Sibley L D
Department of Tropical Medicine and Parasitology, Keio University School of Medicine, Shinjuku, Tokyo, 160, Japan.
Exp Parasitol. 1998 Nov;90(3):277-85. doi: 10.1006/expr.1998.4346.
We have identified type I nucleoside triphosphate hydrolase (NTPase; EC 3.6. 1.3) activity, previously thought to be restricted to the virulent strains of Toxoplasma gondii, in the cell extracts of Neospora caninum tachyzoites. Sequence analysis of a complete cDNA from Nc-1 strain indicated that N. caninum NTPases shared approximately 69% identity to the NTPases of T. gondii and are most similar to the NTPase-I isozyme. Southern blot analysis of genomic DNA and sequence analysis of two independent NTP clones from the Nc-1 strain revealed the presence of multiple genes, at least two of which are transcribed. Substrate specificity and Km values for MgATP2- and MgADP- hydrolysis for recombinant or partially purified native NcNTPase were the same as those for the type I isozyme (NTPase-I). Significantly, no type II enzyme (NTPase-II) activity for NDP hydrolysis was detected in cell extracts of N. caninum, although it is universally present in all T. gondii strains that have been tested. This intriguing difference between these two closely related apicomplexan parasites may provide insight into the function of the NTPases during intracellular parasitism.
我们在犬新孢子虫速殖子的细胞提取物中鉴定出了I型核苷三磷酸水解酶（NTPase；EC 3.6.1.3）活性，此前认为该活性仅限于刚地弓形虫的强毒株。对Nc-1株完整cDNA的序列分析表明，犬新孢子虫NTPases与刚地弓形虫的NTPases约有69%的同一性，且与NTPase-I同工酶最为相似。对基因组DNA的Southern印迹分析以及对Nc-1株两个独立NTP克隆的序列分析显示存在多个基因，其中至少有两个基因被转录。重组或部分纯化的天然NcNTPase对MgATP2-和MgADP-水解的底物特异性和Km值与I型同工酶（NTPase-I）相同。值得注意的是，在犬新孢子虫的细胞提取物中未检测到NDP水解的II型酶（NTPase-II）活性，尽管在所有已测试的刚地弓形虫菌株中普遍存在该活性。这两种密切相关的顶复门寄生虫之间的这种有趣差异可能有助于深入了解NTPases在细胞内寄生过程中的功能。
