Structural basis for the EBA-175 erythrocyte invasion pathway of themalaria parasite Plasmodium falciparum

Tolia NH, Enemark EJ, Sim KL, Joshua-Tor L Cell 122: 183-193, 2005

Structural basis for Duffy recognition by the malaria parasite Duffy-binding–like domain

Singh SK, Hora R, Belrhali H, Chitnis CE, Sharma A

Nature 439: 741-744, 2005

Critical Evaluation of Published Literature BMSD 542, Winter 2006

Background

Plasmodium causes Malaria which affects more than 500 million people and kills about two million annually.

P. falciparum is the most prevalent; P. vivax less so; P. knowlesi is the simian counterpart.

Infection is caused by sporozoites entering into the host bloodstream after a female Anopheles mosquito bite and infecting hepatocytes; the

hepatocytes rupture and release thousands of merozoites each of which can invade an erythrocyte, thus initiating the asexual erythrocytic stage

of the parasite’s life cycle.

All pathological and clinical manifestations of the disease are caused by this critical invasion step.

Background, continued…

Binding to the host endothelium is accomplished through the function of a common adhesion molecule found in two families of parasite ligands.

EBL (erythrocyte binding ligand) family of erythrocyte invasion ligands and the var/PfEMP1 (P. falciparum erythrocyte membrane protein 1)

family of cytoadherence ligands

This adhesive domain, called the Duffy-binding like (DBL) domain was first described as part of the Duffy Binding Protein (DBP), an important

invasion ligand of both P. vivax and P. knowlesi for erythrocytes.

DBL domains contribute to both invasion and cytoadherence and are one of the most versatile and polymorphic adhesive molecules.

X-ray crystallography structures of the DBL domains from two well-studied EBL ligands, the P. knowlesi DBP (PkDBP) and the P.

falciparum EBA-175, have been published.

EBP, EBA, PfEMP, …

Nature 439: 741-744, 2005

EBL, DBL, DBP, PfEMP, …

Cell 122: 183-193, 2005 erythrocyte binding domain (critical)

PkDBP alignments

Nature 439: 741-744, 2005

EBA-175 alignments

Cell 122: 183-193, 2005

PkDBP structure (3 Å)

11 alpha helices, unique fold, three subdomains

Nature 439: 741-744, 2005

EBA-175 structure (2.3 Å)

Cell 122: 183-193, 2005

Binding

DBL domains bind several substrates and have different binding sites, sometimes involving dimerisation.

EBA-175 and PkDBP bind different receptors on the erythrocyte surface.

PkDBL (and PvDBL) bind the host DARC (Duffy antigen receptor for chemokines); mutagenesis data available.

EBA-175, BAEBL, and JSEBL all can bind sialic acid residues, but each recognises different erythrocyte sialoglycoproteins; receptor for EBA-

175 is human RBC receptor glycophorin A. Redundant pathways means that EBA-175 is not essential.

X-ray structure of EBA-175 was solved with sialic acid derivative, alpha-2,3,sialyllactoase to identify the glycan binding site; additional

mutagenesis experiments were performed.

PkDBL binding

Nature 439: 741-744, 2005

PvDBL binding

Nature 439: 741-744, 2005

polymorphic residues in field isolates; immune systemevasion

binding site“just-in-time” releaseand binding to receptor

PkDBL binding

SD1

SD2

SD2DARC bindingsite antigenic

site

antigenicsite

EBA-175 binding

Cell 122: 183-193, 2005

Model for EBA-175 region 2 binding to glycophorin A

Cell 122: 183-193, 2005

Superimposed DBLs (within 2 Å of each other)

DARC bindingsite glycan

bindingsites

A treasure of insights

A treasure of insights

DARC bindingsite

glycan binding

site

Conclusions – insights from x-ray structures

Different sites target different substrates and receptors in different DBL domains

Interplay between sequence conservation and variation to evade immune evasion

For PvDBL, target the DBL-DARC interaction for therapeutics (conserved)

For EBA-175, target the glycan binding sites; distrupt dimersation and/or DBL domain interactions