Nores María J, Prucca César G, Quiroga Rodrigo, Elías Eliana V, Cavallín Lucas, Price Argenta M, Saura Alicia, Carranza Pedro G, Gottig Natalia, Solari Alberto J, Lujan Hugo D
School of Medicine, Catholic University of Córdoba, Jacinto Rios 571, CP5004, Cordoba, Argentina.
Biosci Rep. 2009 Feb;29(1):25-34. doi: 10.1042/BSR20080101.
Giardia lamblia is a medically important protozoan parasite with a basal position in the eukaryotic lineage and is an interesting model to explain the evolution of biochemical events in eukaryotic cells. G. lamblia trophozoites undergo significant changes in order to survive outside the intestine of their host by differentiating into infective cysts. In the present study, we characterize the previously identified Orf-C4 (G. lamblia open reading frame C4) gene, which is considered to be specific to G. lamblia. It encodes a 22 kDa protein that assembles into high-molecular-mass complexes during the entire life cycle of the parasite. ORF-C4 localizes to the cytoplasm of trophozoites and cysts, and forms large spherical aggregates when overexpressed. ORF-C4 overexpression and down-regulation do not affect trophozoite viability; however, differentiation into cysts is slightly delayed when the expression of ORF-C4 is down-regulated. In addition, ORF-C4 protein expression is modified under specific stress-inducing conditions. Neither orthologous proteins nor conserved domains are found in databases by conventional sequence analysis of the predicted protein. However, ORF-C4 contains a region which is similar structurally to the alpha-crystallin domain of sHsps (small heat-shock proteins). In the present study, we show the potential role of ORF-C4 as a small chaperone which is involved in the response to stress (including encystation) in G. lamblia.
蓝氏贾第鞭毛虫是一种在医学上具有重要意义的原生动物寄生虫，在真核生物谱系中处于基础地位，是解释真核细胞生化事件进化的一个有趣模型。蓝氏贾第鞭毛虫滋养体通过分化形成感染性包囊，从而在宿主肠道外生存，在此过程中会发生显著变化。在本研究中，我们对先前鉴定出的Orf-C4（蓝氏贾第鞭毛虫开放阅读框C4）基因进行了表征，该基因被认为是蓝氏贾第鞭毛虫特有的。它编码一种22 kDa的蛋白质，该蛋白质在寄生虫的整个生命周期中组装成高分子量复合物。ORF-C4定位于滋养体和包囊的细胞质中，过表达时会形成大型球形聚集体。ORF-C4的过表达和下调不影响滋养体的活力；然而，当ORF-C4的表达下调时，向包囊的分化会稍有延迟。此外，ORF-C4蛋白表达在特定的应激诱导条件下会发生改变。通过对预测蛋白的常规序列分析，在数据库中未发现直系同源蛋白和保守结构域。然而，ORF-C4包含一个在结构上与小分子热休克蛋白（sHsps）的α-晶状体蛋白结构域相似的区域。在本研究中，我们展示了ORF-C4作为一种小分子伴侣蛋白在蓝氏贾第鞭毛虫应对应激（包括包囊化）过程中的潜在作用。
