Interactions between Merozoite Surface Proteins 1, 6, and 7 of the Malaria ParasitePlasmodium falciparum

Abstract

Merozoites of the malaria parasite Plasmodium falciparum expose at their surface a large multiprotein complex, composed of proteolytically processed, noncovalently associated products of at least three genes, msp-1, msp-6, and msp-7. During invasion of erythrocytes, this complex is shed from the surface except for a small glycosylphosphatidylinositol-anchored portion originating from MSP-1. The proteolytic cleavage separating the C-terminal portion of MSP-1 is required for successful invasion. Little is known about the structure and function of the abundant and essential multipartite complex. Using heterologously produced MSP-1, MSP-6, and MSP-7 in precursor and with the exception of MSP-7 in processed form, we have studied in vitro the complex formation between the different proteins to identify the interaction partners within the complex. Both MSP-6 36 and MSP-7 bind only to MSP-1 subunits that are shed, but although MSP-6 36 contacts just subunit p38, MSP-7 interacts with p83, p30, and p38. The intact C-terminal region of MSP-6 is required for the association with p38 as well as for its multimerization into tetramers. Furthermore, our data suggest that only the processed form and not the precursor form of MSP-1 interacts with MSP-6 36 . MSP-6-as well as MSP-7-specific rabbit antibodies inhibit parasite multiplication in vitro as shown previously for antibodies directed against MSP-1. Our findings raise interesting questions with regard to proteolysis-mediated mechanisms of maturation of the MSP-1-MSP-6-MSP-7 complex and to the mode by which antibodies directed against this complex interfere with parasite multiplication.

Insights into Duffy Binding-like Domains through the Crystal Structure and Function of the Merozoite Surface Protein MSPDBL2 from Plasmodium falciparum

“…Both PfMSPDBL1 and -2 have potential PfSUB1 cleavage sites located near to their N terminus, and processing by this protease would produce fragments of similar size to those observed for the processed forms of these proteins. A similar PfSUB1 processing event is required for incorporation of MSP6, another member of the MSP3 family, into the MSP1 complex (40,41). It is possible that unprocessed forms of PfMSPDBL1 and -2, which are not incorporated into the merozoite surface (supplemental Fig.…”

Identification and Prioritization of Merozoite Antigens as Targets of Protective Human Immunity to Plasmodium falciparum Malaria for Vaccine and Biomarker Development

“…The quality of protein expression and folding had been validated previously for some of the protein constructs used by demonstrating that vaccine-induced Abs raised against the recombinant protein recognize native protein (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37); vaccine-induced Abs have functional antiparasite activity in growthinhibition assays (GIAs) or Ab-dependent cellular-inhibition (ADCI) assays (12,28,30,(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43); or the recombinant protein has appropriate biological function by binding its receptor (25,28,34,35,38,39) (Supplemental Table I). Validation of WGCF as an appropriate system for expression of P. falciparum merozoite proteins has also been established in several ways.…”

A Key Role for Plasmodium Subtilisin-like SUB1 Protease in Egress of Malaria Parasites from Host Hepatocytes

“…In P. falciparum, PfMSP1 interacts with other MSPs, PfMSP6 and -7, forming a complex on the merozoite surface (46 -48). PfSUB1 matures the three components of this complex (21), which remains associated at the surface of the merozoite and is critical for merozoite invasion, probably via a merozoite-erythrocyte attachment step, prior to parasite reorientation and internalization inside the host cell (23,49,50). More work is needed to unravel the complex basis of merozoite attachment to the erythrocyte and protein maturation events involved in the process.…”

“…The reported role of SUB1 in P. falciparum merozoite invasion is to undertake the processing of merozoite surface proteins (MSPs), including MSP1, the major merozoite surface protein and a leading malaria vaccine candidate (21). After SUB1 maturation, the membrane-anchored C-terminal 42-kDa fragment of MSP1 remains associated with the other MSP1 fragments and additional partners, including MSP6 and MSP7 (21,23), which are also processed by SUB1 (21). Although functional studies suggest that MSPs promote initial binding of the merozoite to the erythrocyte surface, their exact function remains unclear.…”