Anant S, Martin S A, Yu H, MacGinnitie A J, Devaney E, Davidson N O
Department of Medicine, University of Chicago, IL 60637, USA.
Mol Biochem Parasitol. 1997 Sep;88(1-2):105-14. doi: 10.1016/s0166-6851(97)00083-2.
A number of genes have been identified that are highly expressed in the post-infective L3 stage of the filarial parasite, Brugia pahangi. Amongst these was a cDNA with homology to the cytidine deaminase (CDD) gene family. Phylogenetic analysis of the various cytosine nucleoside deaminases suggest that Brugia pahangi CDD evolved with significant divergence from the RNA editing family. In order to characterize its function, we have expressed Brugia pahangi CDD in bacteria as a chimera with maltose-binding protein (MBP). Biochemical analysis demonstrates the MBP-CDD fusion protein functions as an authentic cytidine deaminase with an obligate requirement for zinc. In addition to cytidine deaminase activity, however, the fusion protein demonstrates RNA binding activity with specificity for AU-rich sequences and was found to bind an RNA template spanning the edited site of mammalian apolipoprotein B (apoB) mRNA. This RNA binding activity was not found in two different recombinant bacterial CDD proteins. In vitro RNA editing assays revealed that MBP-CDD failed to mediate cytidine deamination of a mammalian apoB RNA template. Furthermore, binding of MBP-CDD to the apoB RNA did not inhibit in vitro editing of this template by apobec-1. The data suggest that the cytosine nucleoside deaminases and RNA editing deaminases have acquired different mechanisms of binding to an AU-rich RNA template, presumably with different functional implications.
已经鉴定出一些在丝状寄生虫彭亨布鲁线虫感染后的L3阶段高表达的基因。其中有一个与胞苷脱氨酶（CDD）基因家族具有同源性的cDNA。对各种胞嘧啶核苷脱氨酶的系统发育分析表明，彭亨布鲁线虫CDD与RNA编辑家族的进化存在显著差异。为了表征其功能，我们已在细菌中表达了彭亨布鲁线虫CDD，它是与麦芽糖结合蛋白（MBP）的嵌合体。生化分析表明，MBP - CDD融合蛋白作为一种真正的胞苷脱氨酶发挥作用，对锌有绝对需求。然而，除了胞苷脱氨酶活性外，该融合蛋白还表现出对富含AU序列具有特异性的RNA结合活性，并且发现它能结合跨越哺乳动物载脂蛋白B（apoB）mRNA编辑位点的RNA模板。在两种不同的重组细菌CDD蛋白中未发现这种RNA结合活性。体外RNA编辑试验表明，MBP - CDD未能介导哺乳动物apoB RNA模板的胞苷脱氨作用。此外，MBP - CDD与apoB RNA的结合并不抑制载脂蛋白B编辑酶1（apobec - 1）对该模板的体外编辑。数据表明，胞嘧啶核苷脱氨酶和RNA编辑脱氨酶获得了与富含AU的RNA模板结合的不同机制，推测具有不同的功能意义。
