A Common Cross-species Function for the Double Epidermal Growth Factor-like Modules of the Highly Divergent Plasmodium Surface Proteins MSP-1 and MSP-8

Abstract

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 that Plasmodium falciparum parasites 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 from P. berghei MSP-8, the sequence of which shares only low identity with its MSP-1 counterpart. Hence, the C-terminal EGF domains of at least some Plasmodium surface proteins appear to perform the same function in asexual bloodstage 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 from P. falciparum and P. chabaudi MSP-1 were also not capable of replacing the P. falciparum MSP-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.

Variation in use of erythrocyte invasion pathways by Plasmodium falciparum mediates evasion of human inhibitory antibodies

“…Acquired inhibitory antibodies have also been reported for MSP1 (35,41) and AMA1 (42), but we found that the ability of these antibodies to inhibit invasion did not change with variation in invasion pathways. In previous studies, targeted disruption of other merozoite proteins, RAP1, MSP5, and MSP8, had no effect on invasion phenotypes (43)(44)(45). This suggests that other antibody specificities would not account for the differential inhibition of parasite lines with different invasion phenotypes.…”

“…Analysis of flow cytometry data was performed using FlowJo software (Tree Star Inc.). Antibodies against MSP119 (raised against GST fusion protein) used in the assays (at 1:10 final dilution) were generated by vaccination of rabbits and were kindly provided by Brendan Crabb (Walter and Eliza Hall Institute of Medical Research) (44). Samples from nonexposed donors were included as negative controls in all assays, and anti-MSP1 and/or anti-AMA1 antibodies acted as a positive control.…”

A new release on life: emerging concepts in proteolysis and parasite invasion

“…As mentioned above, there are indications that the C-terminal part of MSP1 binds directly or indirectly to host cell receptors at invasion (Goel et al, 2003;Li et al, 2004), but no hint that this requires -or is enhanced by -secondary processing. Furthermore, recent work by Crabb and colleagues showing that the P. falciparum and Plasmodium chabaudi MSP-1 19 domains can be replaced by even highly divergent sequences without any detrimental effect on parasite replication argues for a predominantly structural role for MSP-1 19 (O'Donnell et al, 2000;Drew et al, 2004).…”

Evaluation of the Immunogenicity and Vaccine Potential of Recombinant Plasmodium falciparum Merozoite Surface Protein 8

“…This is unusual given that many of the MSPs implicated in the invasion process are expressed in maturing schizonts (9). Nevertheless, the EGF-like domains of PfMSP1 can be replaced with those of P. berghei MSP8 with no apparent effect on the in vitro growth of the transgenic P. falciparum parasites (20).…”