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

Diego Garzón-Ospina,Johanna Forero-Rodríguez,Manuel A Patarroyo

doi:10.1186/s12862-016-0830-x

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.

Highlights

The merozoite surface protein 7 (MSP7) is a Plasmodium protein which is involved in parasite invasion; the gene encoding it belongs to a multigene family
Multigene families might evolve in line with a concerted or birth-and-death evolutionary model [3]; paralogous genes keep the same function in the former due to gene conversion whilst paralogous genes could lose or acquire a new function in a birth-and-death model
MSP7 is a merozoite surface protein encoded by a gene belonging to a multigene family located in chromosome 13 in hominidand rodent-parasites but in chromosome 12 in monkeyparasites

Summary

Introduction

The merozoite surface protein 7 (MSP7) is a Plasmodium protein which is involved in parasite invasion; the gene encoding it belongs to a multigene family. MSP7 is a merozoite surface protein encoded by a gene belonging to a multigene family located in chromosome 13 in hominidand rodent-parasites but in chromosome 12 in monkeyparasites. This family has a different copy number amongst Plasmodium species [15, 16]. Functional assays have shown that P. falciparum MSP7 (MSP7I) is proteolytically processed; the resulting 22 kDa C-terminal region fragment is not covalently associated with MSP1 [7] and has cross-reactivity with other MSP7 proteins [17] This fragment appears be involved in invasion by binding to red blood cells [21]. The MSP7 knockout reduces the normal growth rate of the mutant parasite in P. berghei; it becomes restored a few days later [22]

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