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.
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