Alexandre Jean Sf, Kaewthamasorn Morakot, Yahata Kazuhide, Nakazawa Shusuke, Kaneko Osamu
Department of Protozoology, Institute of Tropical Medicine (NEKKEN) and the Global COE Program, Nagasaki University, Sakamoto, Nagasaki 852-8523, Japan.
Trop Med Health. 2011 Sep;39(3):77-82. doi: 10.2149/tmh.2011-12. Epub 2011 Sep 30.
A protein complex of high-molecular-mass proteins (PfRhopH) of the human malaria parasite Plasmodium falciparum induces host protective immunity and therefore is a candidate for vaccine development. Clarification of the level of polymorphism and the evolutionary processes is important both for vaccine design and for a better understanding of the evolution of cell invasion in this parasite. In a previous study on 5 genes encoding RhopH1/Clag proteins, positive diversifying selection was detected in clag8 and clag9 but not in the paralogous clag2, clag3.1 and clag3.2. In this study, to extend the analysis of clag polymorphism, we obtained sequences surrounding the most polymorphic regions of clag2, clag8, and clag9 from parasites collected in Thailand. Using sequence data obtained newly in this study and reported previously, we classified clag2 sequences into 5 groups based on the similarity of the deduced amino acid sequences and number of insertions/deletions. By the sliding window method, an excess of nonsynonymous substitutions over synonymous substitutions was detected in the group 1 and group 2 clag2 and clag8 sequences. Population-based analyses also detected a significant departure from the neutral expectation for group 1 clag2 and clag8. Thus, two independent approaches suggest that clag2 is subject to a positive diversifying selection. The previously suggested positive selection on clag8 was also supported by population-based analyses. However, the positive selection on clag9, which was detected by comparing the 5 sequences, was not detected using the additional 34 sequences obtained in this study.
人类疟原虫恶性疟原虫的高分子量蛋白质（PfRhopH）蛋白复合物可诱导宿主保护性免疫，因此是疫苗开发的候选对象。阐明多态性水平和进化过程对于疫苗设计以及更好地理解该寄生虫细胞入侵的进化都很重要。在先前一项针对5个编码RhopH1/Clag蛋白的基因的研究中，在clag8和clag9中检测到正向多样化选择，但在同源的clag2、clag3.1和clag3.2中未检测到。在本研究中，为了扩展对clag多态性的分析，我们从泰国收集的寄生虫中获得了clag2、clag8和clag9最具多态性区域周围的序列。利用本研究新获得的和先前报道的序列数据，我们根据推导的氨基酸序列的相似性和插入/缺失的数量将clag2序列分为5组。通过滑动窗口法，在第1组和第2组clag2和clag8序列中检测到非同义替换超过同义替换。基于群体的分析也检测到第1组clag2和clag8显著偏离中性预期。因此，两种独立的方法表明clag2受到正向多样化选择。基于群体的分析也支持先前提出的对clag8的正向选择。然而，通过比较5个序列检测到的对clag9的正向选择，在使用本研究获得的另外34个序列时未检测到。
