Evidence of functional divergence in MSP7 paralogous proteins: a molecular-evolutionary and phylogenetic analysis

Abstract

BackgroundThe merozoite surface protein 7 (MSP7) is a Plasmodium protein which is involved in parasite invasion; the gene encoding it belongs to a multigene family. It has been proposed that MSP7 paralogues seem to be functionally redundant; however, recent experiments have suggested that they could have different roles.ResultsThe msp7 multigene family has been described in newly available Plasmodium genomes; phylogenetic relationships were established in 12 species by using different molecular evolutionary approaches for assessing functional divergence amongst MSP7 members. Gene expansion and contraction rule msp7 family evolution; however, some members could have had concerted evolution. Molecular evolutionary analysis showed that relaxed and/or intensified selection modulated Plasmodium msp7 paralogous evolution. Furthermore, episodic diversifying selection and changes in evolutionary rates suggested that some paralogous proteins have diverged functionally.ConclusionsEven though msp7 has mainly evolved in line with a birth-and-death evolutionary model, gene conversion has taken place between some paralogous genes allowing them to maintain their functional redundancy. On the other hand, the evolutionary rate of some MSP7 paralogs has become altered, as well as undergoing relaxed or intensified (positive) selection, suggesting functional divergence. This could mean that some MSP7s can form different parasite protein complexes and/or recognise different host receptors during parasite invasion. These results highlight the importance of this gene family in the Plasmodium genus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0830-x) contains supplementary material, which is available to authorized users.

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“…Evidence of episodic positive selection was found in some parasite lineages (Additional file 2 : Figure S2). As shown for other antigens [ 49 – 51 ], the episodic selection found in GAMA could be the outcome of adaptation to different hosts during malaria-primate evolution [ 50 , 51 ]. Therefore, the insertions found in P. vivax could be an adaptation of the species to humans since the RR in malaria are associated with evasion of the host’s immune response, making such response become directed against functionally unimportant regions [ 52 , 53 ].…”

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