Processing of Plasmodium falciparum Merozoite Surface Protein MSP1 Activates a Spectrin-Binding Function Enabling Parasite Egress from RBCs

Abstract

SummaryThe malaria parasite Plasmodium falciparum replicates within erythrocytes, producing progeny merozoites that are released from infected cells via a poorly understood process called egress. The most abundant merozoite surface protein, MSP1, is synthesized as a large precursor that undergoes proteolytic maturation by the parasite protease SUB1 just prior to egress. The function of MSP1 and its processing are unknown. Here we show that SUB1-mediated processing of MSP1 is important for parasite viability. Processing modifies the secondary structure of MSP1 and activates its capacity to bind spectrin, a molecular scaffold protein that is the major component of the host erythrocyte cytoskeleton. Parasites expressing an inefficiently processed MSP1 mutant show delayed egress, and merozoites lacking surface-bound MSP1 display a severe egress defect. Our results indicate that interactions between SUB1-processed merozoite surface MSP1 and the spectrin network of the erythrocyte cytoskeleton facilitate host erythrocyte rupture to enable parasite egress.

Parasitophorous vacuole poration precedes its rupture and rapid host erythrocyte cytoskeleton collapse in Plasmodium falciparum egress

“…Examination by electron tomography showed that the parasites in the C1-treated preparation fell into three broad groups: those in which segmentation (merozoite budding) had not begun (as indicated by a single multinucleated parasite, with a single membrane underlying the PVM), those at a stage of partial segmentation (in which the daughter merozoites are partially separated but still attached), and those (the majority) in which segmentation was complete, producing fully separated daughter merozoites. Importantly, all of the C1-blocked schizonts examined displayed an intact PVM, in accord with previous evidence that PKG inhibitors potently stall egress at a stage before rounding up and PVM rupture (10,14,28,41). Consistent with this, in all partially segmented schizonts we observed a clear contrast difference between the material in the vacuole and the material in the blood cell cytosol, with the red cell cytosol displaying a darker, more electron-dense appearance than the contents of the PV (Fig.…”

“…The selective PKG inhibitors compound 1 (C1) and compound 2 (C2) reversibly inhibit egress before the rounding up stage (10,14,28,41). In contrast, treatment with the broad-spectrum cysteine protease inhibitor E64 allows PVM rupture but selectively prevents erythrocyte membrane rupture, resulting in merozoites trapped in the blood cell after rupture of the PVM (30,42).…”

“…SUB1 has several targets, including a multiprotein merozoite surface complex called MSP1/6/7 and a set of soluble papain-like PV proteins called the SERA family (15)(16)(17)(18) that have been implicated in egress in the blood, liver, and mosquito stages of the parasite life cycle (19)(20)(21)(22). Processing of the MSP1/6/7 complex is necessary for efficient escape from the erythrocyte through interaction of SUB1-processed MSP1 on the surface of the merozoites with spectrin of the host erythrocyte cytoskeleton (10). Proteolytic processing by SUB1 of the Significance Malaria parasites develop within red blood cells inside a membraneenclosed parasitophorous vacuole.…”

Multiple Plasmodium falciparum Merozoite Surface Protein 1 Complexes Mediate Merozoite Binding to Human Erythrocytes

“…It has also been shown that blocking processing of MSP1 blocks egress, where unprocessed MSP1 is not able to bind to spectrin and is subsequently unable to destabilize the erythrocyte cytoskeleton for egress (46). It thus appears that the secondary processing of MSP1 is quite sensitive to interactions of the complex with antibodies during schizogony and also the egress of parasites for invasion, revealing at least two possible mechanisms for interference in parasite growth.…”

“…The most abundant MSP on the parasite surface is MSP1, and it plays an essential role for parasite survival (1). Recent work has shown that the processing of MSP1 not only produces mature MSP1 fragments important for parasite viability but also appears to be important for parasite egress (46). Although the precise role of MSP1 during invasion has not been described, it is known that processed MSP1 binds to multiple peripheral merozoite surface proteins to form large macromolecular structures on the parasite (16,17,47).…”