Briones M R, Egima C M, Eichinger D, Schenkman S
Departamento de Microbiologia, Imunologia e Parasitologia, Escola Paulista de Medicinia, São Paulo, S.P. Brasil.
J Mol Evol. 1995 Aug;41(2):120-31. doi: 10.1007/BF00170663.
The trans-sialidase of Trypanosoma cruzi mammalian forms transfers sialic acids from host's cell-surface glycoconjugates to acceptor molecules on parasite cell surface. To investigate the mechanism by which the mammalian stages of Trypanosoma cruzi have acquired their trans-sialidase, we compared the nucleotide and predicted amino acid sequences of trans-sialidase genes expressed in different developmental stages and strains of Trypanosoma cruzi with the sialidase gene of Trypanosoma rangeli and the sialidase genes of the prokaryotic genera Clostridium, Salmonella, and Actinomyces. The trans-sialidase gene products of Trypanosoma cruzi have a significant degree of structural and biochemical similarity to the sialidases found in bacteria and viruses, which would hint that horizontal gene transfer occurred in Trypanosoma cruzi trans-sialidase evolutionary history. The comparison of inferred gene trees with species trees suggests that the genes encoding the T. cruzi trans-sialidase of mammalian forms might be derived from genes expressed in the insect forms of the genus Trypanosoma. The branching order of trees inferred from T. cruzi trans-sialidase sequences, the sialidase from Trypanosoma rangeli, and bacterial sialidases parallels the expected branching order of the species and suggests that the divergence times of these sequences are remarkably long. Therefore, a "vertical" inheritance from a hypothetical eukaryotic trans-sialidase gene expressed in insect forms of trypanosomes is more likely to have occurred than the horizontal gene transfer from bacteria, and thus explains the presence of this enzyme in the mammalian infective forms of Trypanosoma cruzi.
克氏锥虫哺乳动物型的转唾液酸酶将宿主细胞表面糖缀合物上的唾液酸转移至寄生虫细胞表面的受体分子上。为了研究克氏锥虫哺乳动物阶段获得其转唾液酸酶的机制，我们将克氏锥虫不同发育阶段和菌株中表达的转唾液酸酶基因的核苷酸序列和预测的氨基酸序列，与兰氏锥虫的唾液酸酶基因以及原核生物属梭菌属、沙门氏菌属和放线菌属的唾液酸酶基因进行了比较。克氏锥虫的转唾液酸酶基因产物与细菌和病毒中的唾液酸酶在结构和生化方面有显著程度的相似性，这暗示在克氏锥虫转唾液酸酶的进化历史中发生了水平基因转移。将推断的基因树与物种树进行比较表明，编码克氏锥虫哺乳动物型转唾液酸酶的基因可能源自锥虫属昆虫型中表达的基因。从克氏锥虫转唾液酸酶序列、兰氏锥虫的唾液酸酶序列和细菌唾液酸酶推断出的树的分支顺序与预期的物种分支顺序相似，这表明这些序列的分歧时间非常长。因此，与从细菌进行水平基因转移相比，从锥虫昆虫型中表达的假定真核转唾液酸酶基因进行“垂直”遗传的可能性更大，从而解释了这种酶在克氏锥虫哺乳动物感染型中的存在。
