Limited genetic diversity of N-terminal of merozoite surface protein-1 (MSP-1) in Plasmodium ovale curtisi and P. ovale wallikeri imported from Africa to China

Ruilin Chu,Limei Chen,Guoding Zhu,Xinxin Zhang,Yinghua Xuan,Jing Chen,Yang Cheng,Sui Xu,Jun Cao,Yuhong Li,Jianxia Tang

doi:10.1186/s13071-018-3174-0

Abstract

BackgroundPlasmodium merozoite surface protein-1 (MSP-1) is released into the bloodstream during merozoite invasion, and thus represents a crucial malarial vaccine target. Although substantial research effort has been devoted to uncovering the genetic diversity of MSP-1 for P. falciparum and P. vivax, there is minimal information available regarding the genetic profiles and structure of P. ovale. Therefore, the aim of the present study was to determine the extent of genetic variation among two subspecies of P. ovale by characterizing the MSP-1 N-terminal sequence at the nucleotide and protein levels.MethodsN-terminal of MSP-1 gene were amplified from 126 clinical samples collected from imported cases of malaria in migrant workers returning to Jiangsu Province from Africa using a conventional polymerase chain reaction (PCR) assay. The PCR products were then sequenced and analyzed using the GeneDoc, MegAlign, MEGA7 and DnaSP v.6 programs.ResultsThe average pairwise nucleotide diversities (π) of P. ovale curtisi and P. ovale wallikeri MSP-1 genes (pomsp1) were 0.01043 and 0.01974, respectively, and the haplotype diversity (Hd) were 0.746 and 0.598, respectively. Most of the nucleotide substitutions detected were non-synonymous, indicating that the genetic variations of pomsp1 were maintained by positive diversifying selection, thereby suggesting their role as a potential target of a protective immune response. Amino acid substitutions of P. ovale curtisi and P. ovale wallikeri MSP-1 could be categorized into five and three unique amino acid variants, respectively.ConclusionsLow mutational diversity was observed in pomsp1 from the Jiangsu Province imported malaria cases; further studies will be developed such as immunogenicity and functional analysis.

Highlights

Plasmodium merozoite surface protein-1 (MSP-1) is released into the bloodstream during merozoite invasion, and represents a crucial malarial vaccine target
Characterization of PoMSP-1 The lengths of Merozoites surface proteins (MSPs)-1 encoded by the full-length P. ovale curtisi (GenBank: KC137343) and P. ovale wallikeri (GenBank: KC137341) genes were 1727 and 1672, respectively, each beginning with a predicted 19 aa signal peptide sequence
Similar to PvMSP-1 and PfMSP-1, some other specific regions were identified in the P. ovale curtisi predicted protein primary structure, such as a coiled-coil region, Pfam region, and EGF domains (Fig. 2a)

Summary

Introduction

Plasmodium merozoite surface protein-1 (MSP-1) is released into the bloodstream during merozoite invasion, and represents a crucial malarial vaccine target. The aim of the present study was to determine the extent of genetic variation among two subspecies of P. ovale by characterizing the MSP-1 N-terminal sequence at the nucleotide and protein levels. Five species in the genus Plasmodium (P. falciparum, P. vivax, P. malariae, P. ovale and P. knowlesi) are known to cause. In Africa, only 0.7–10% of human malaria cases are caused by P. ovale infections; the diagnosis of P. ovale is often overlooked due to the low levels of parasitemia and mixed-species malaria infections [7, 9]. Approximately 300 malaria cases in China imported from Africa annually are caused by P. ovale. There are two subspecies of P. ovale, P. ovale curtisi (classical type) and P. ovale wallikeri (variant type) [10], which show dimorphism of multiple genetic loci [2]

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