Epidermal growth factor-like motifs 1 and 2 of Plasmodium vivax merozoite surface protein 1 are critical domains in erythrocyte invasion

An understanding of structural and functional constraints on the C-terminal double epidermal growth factor (EGF)-like modules of merozoite surface protein (MSP)-1 and related proteins is of importance to the development of these molecules as malaria vaccines and drug targets. Using allelic replacement, we show thatPlasmodium falciparumparasites can invade erythrocytes and grow efficiently in the absence of an MSP-1 protein with authentic MSP-1 EGF domains. In this mutant parasite line, the MSP-1 EGFs were replaced by the corresponding double EGF module fromP. bergheiMSP-8, the sequence of which shares only low identity with its MSP-1 counterpart. Hence, the C-terminal EGF domains of at least somePlasmodiumsurface proteins appear to perform the same function in asexual blood-stage development. Mapping the surface location of the few residues that are common to these functionally complementary EGF modules revealed the presence of a highly conserved pocket of potential functional significance. In contrast to MSP-8, an even more divergent double EGF module, that from the sexual stage protein PbS25, was not capable of complementing MSP-1 EGF function. More surprisingly, two chimeric double EGF modules comprising hybrids of the EGF domains fromP. falciparumandP. chabaudiMSP-1 were also not capable of replacing theP. falciparumMSP-1 EGF module. Together, these data suggest that although the MSP-1 EGFs can accommodate extensive sequence diversity, there appear to be constraints that may restrict the simple accumulation of point mutations in the face of immune pressure in the field.

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Comparison of Immunogenicities of Recombinant Plasmodium vivax Merozoite Surface Protein 1 19- and 42-Kilodalton Fragments Expressed in Escherichia coli

Infection and Immunity ◽

10.1128/iai.72.10.5775-5782.2004 ◽

2004 ◽

Vol 72 (10) ◽

pp. 5775-5782 ◽

Cited By ~ 42

Author(s):

Suraksha Sachdeva ◽

Gul Ahmad ◽

Pawan Malhotra ◽

Paushali Mukherjee ◽

V. S. Chauhan

Keyword(s):

Escherichia Coli ◽

Plasmodium Vivax ◽

Expression System ◽

Surface Protein ◽

Merozoite Surface Protein ◽

Interleukin 4 ◽

Specific Response ◽

Immunological Responses ◽

Merozoite Surface Protein 1 ◽

Epidermal Growth

ABSTRACT The 42- and 19-kDa C-terminal fragments of merozoite surface protein 1 (MSP-142 and MSP-119, respectively) are both promising blood-stage vaccine candidate antigens. At present, it is not clear which of the two antigens will be more suitable for inclusion in a cocktail malaria vaccine. In the present study, we expressed the two C-terminal fragments of Plasmodium vivax MSP-1 (PvMSP-1) in an Escherichia coli expression system and purified them by using a rapid two-step protocol. Both of the products were recognized by monoclonal antibodies against PvMSP-1 as well as by immune sera from several individuals exposed to P. vivax. We analyzed and compared the immunological responses to recombinant PvMSP-119 and PvMSP-142 in mice by using six different adjuvant formulations. Moderate to high antibody responses were observed with both of the antigens in different adjuvant formulations. Surprisingly, alum, which is generally considered to be a poor adjuvant for recombinant malaria antigens, was found to be as good an adjuvant as Montanide ISA 720, ASO2A, and other adjuvant formulations. Most adjuvant formulations induced high levels of immunoglobulin G1 (IgG1), followed by IgG3 and IgG2. Lymphocytes from animals in the PvMSP-142- and PvMSP-119-immunized groups showed proliferative responses upon stimulation with the respective antigens, and high levels of interleukin-4 (IL-4), IL-5, and gamma interferon were detected in the culture supernatants. Immunodepletion studies with sera from mice immunized with these two antigens showed that while immunization with PvMSP-142 does produce a PvMSP-119-specific response, a substantial portion is also focused on structures in PvMSP-142 not represented by the epidermal growth factor-like domains of PvMSP-119. These findings may have implications for the design of MSP-1-based vaccine constructs.

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