Plasmodium falciparum BAEBL Binds to Heparan Sulfate Proteoglycans on the Human Erythrocyte Surface

Abstract

Erythrocyte invasion is critical to the pathogenesis and survival of the malarial parasite, Plasmodium falciparum. This process is partly mediated by proteins that belong to the Duffy binding-like family, which are expressed on the merozoite surface. One of these proteins, BAEBL (also known as EBA-140), is thought to bind to glycophorin C in a sialic acid-dependent manner. In this report, by the binding assay between recombinant BAEBL protein and enzyme-treated erythrocytes, we show that the binding of BAEBL to erythrocytes is mediated primarily by sialic acid and partially through heparan sulfate (HS). Because BAEBL binds to several kinds of HS proteoglycans or purified HS, the BAEBL-HS binding was found to be independent of the HS proteoglycan peptide backbone and the presence of sialic acid moieties. Furthermore, both the sialic acid-and HS-dependent binding were disrupted by the addition of soluble heparin. This inhibition may be the result of binding between BAEBL and heparin. Invasion assays demonstrated that HS-dependent binding was related to the efficiency of merozoite invasion. These results suggest that HS functions as a factor that promotes the binding of BAEBL and merozoite invasion. Moreover, these findings may explain the invasion inhibition mechanisms observed following the addition of heparin and other sulfated glycoconjugates.Malaria caused by Plasmodium falciparum kills approximately 1 million people per year. After entering the human bloodstream, the parasite propagates asexually via repeated cycles of erythrocyte invasion, cell division, and cell rupture. The process by which the parasitic merozoites invade erythrocytes involves the following steps: attachment, apical reorientation, junction formation, and the formation of a protective parasitophorous vacuole (1).The Duffy binding-like (DBL) 2 family is composed of adhesion molecules that are critical for junction formation between the apical end of the merozoite and the erythrocyte surface.Proteins in this family, such as EBA-175 (erythrocyte-binding antigen-175), are homologous to Plasmodium vivax Duffybinding protein. These proteins contain one or more DBL domains, which are composed of conserved cysteine residues and are associated with erythrocyte binding (2). EBA-175 is bound to glycophorin A on the erythrocyte surface in a sialic acid-dependent manner (3). However, erythrocytes that are treated with neuraminidase remain susceptible to the merozoites of some clones (4), indicating the existence of sialic acidindependent invasion pathways. These alternative pathways are thought to be mediated, at least in part, by other members of the DBL family (5).Parasite growth is inhibited by the addition of heparin, some sulfated saccharide anions, and sulfated chemical compounds (6 -11). Although the inhibition mechanisms remain unclear, these reports suggest the possibility that sulfated moieties play a role in merozoite invasion. In addition to invasion, heparan sulfate (HS) is believed to function as a receptor for PfEMP1 (P. falciparum erythr...

Interactions with heparin-like molecules during erythrocyte invasion by Plasmodium falciparum merozoites

“…There may be other interactions between merozoite proteins and heparin-like molecules that are also important during invasion. It was recently reported that PfRh5 47 and BAEBL/EBA140 48 have some heparin-binding activity. However, further studies are needed to confirm the specificity and relevance of these interactions, and EBA140 appears to function predominantly by binding glycophorin C. 2,43 Live imaging revealed that inhibition of invasion by heparin occurred before tight-junction formation when the EBAs and PfRh proteins are thought to act.…”

Molecular Basis for Sialic Acid-dependent Receptor Recognition by the Plasmodium falciparum Invasion Protein Erythrocyte-binding Antigen-140/BAEBL

“…Heparitinase treatment of erythrocytes inhibits RII PfEBA-140 binding, providing support for a potential interaction with cell surface GAGs such as heparan sulfate (23). These observations suggest that GAGs on the erythrocyte surface interact with PfEBA-140 and may promote invasion.…”

“…The effect of mutating motif 2 has not been examined. In contrast to the adjacent motifs 1 and 4, mutation of sulfate-binding motifs 3 and 5, which are distal to the glycan-binding sites, has little or no effect on erythrocyte binding (23). Thus, it is plausible that sulfate-binding sites 1, 2, and 4 represent true interaction elements that may play a role in facilitating invasion.…”

“…Recent evidence suggests that binding to glycosaminoglycans (GAGs) on the erythrocyte surface promotes merozoite invasion (22). PfEBA-140 is capable of binding heparin, and it has been proposed that cell surface GAGs may function as a secondary interaction element during PfEBA-140-mediated invasion (23).…”

Affinity-Based Methods for the Separation of Parasite Proteins

“…The first step involves the recognition of molecules at the surface of the target cell, which triggers the activation of signaling pathways that are implicated in the parasite internalization (Abban & Meneses 2010;Epting et al, 2011). Host cell surface sulfated proteoglycans have been implicated as key molecules at the host cell-parasite interface, mediating the adhesion and invasion of numerous parasitic microorganisms (Jacquet et al, 2001;Kobayashi et al, 2010;O'Donnell & Shukla 2010).…”