Structural Basis for the ABO Blood-Group Dependence of Plasmodium falciparum Rosetting

Inès Vigan-Womas,Jacques H Cohen,Micheline Guillotte,Odile Mercereau-Puijalon,Thierry Peyrard,Bertrand Raynal,Alexandre Juillerat,Patrick England,Audrey Hessel,Graham A Bentley,Anita Lewit-Bentley,Olivier Bertrand

doi:10.1371/journal.ppat.1002781

Abstract

The ABO blood group influences susceptibility to severe Plasmodium falciparum malaria. Recent evidence indicates that the protective effect of group O operates by virtue of reduced rosetting of infected red blood cells (iRBCs) with uninfected RBCs. Rosetting is mediated by a subgroup of PfEMP1 adhesins, with RBC binding being assigned to the N-terminal DBL1α1 domain. Here, we identify the ABO blood group as the main receptor for VarO rosetting, with a marked preference for group A over group B, which in turn is preferred to group O RBCs. We show that recombinant NTS-DBL1α1 and NTS-DBL1α1-CIDR1γ reproduce the VarO-iRBC blood group preference and document direct binding to blood group trisaccharides by surface plasmon resonance. More detailed RBC subgroup analysis showed preferred binding to group A1, weaker binding to groups A2 and B, and least binding to groups Ax and O. The 2.8 Å resolution crystal structure of the PfEMP1-VarO Head region, NTS-DBL1α1-CIDR1γ, reveals extensive contacts between the DBL1α1 and CIDR1γ and shows that the NTS-DBL1α1 hinge region is essential for RBC binding. Computer docking of the blood group trisaccharides and subsequent site-directed mutagenesis localized the RBC-binding site to the face opposite to the heparin-binding site of NTS-DBLα1. RBC binding involves residues that are conserved between rosette-forming PfEMP1 adhesins, opening novel opportunities for intervention against severe malaria. By deciphering the structural basis of blood group preferences in rosetting, we provide a link between ABO blood grouppolymorphisms and rosette-forming adhesins, consistent with the selective role of falciparum malaria on human genetic makeup.

Highlights

The ABO blood group system of carbohydrate antigen expression on the surface of human red blood cells (RBCs) is critically important in transfusion medicine
We show that the Head region binds RBCs more efficiently than NTS-DBL1a1 and that ABO blood group polymorphisms influence binding of both domains
We localize the RBC-binding site to the face opposite to the heparin-binding site of NTS-DBL1a1 and document direct binding of the Head region to A and B trisaccharides These findings provide novel insights into the interactions established by malaria parasites with a prominent human blood group

Summary

Introduction

The ABO blood group system of carbohydrate antigen expression on the surface of human red blood cells (RBCs) is critically important in transfusion medicine. The best-documented parasite determinant associated with the ABO blood group is rosetting, the capacity of infected RBCs to bind uninfected RBCs, which is consistently associated with severe malaria in African children [10,11,12] and is reduced inblood group O individuals [9,12,13,14,15,16]. The rosette-forming PfEMP1 adhesins described so far, namely IT4/R29 [23], Palo Alto 89F5 VarO [24], 3D7/PF13_0003 [25] and IT4/var60 [26], belong to a specific sub-group called groupA/UpsA var genes and, interestingly, all four present a specific DBL1a1-CIDR1c double domain Head region [19]. Analysis of pseudo-rosettes formed on the surface of COS cells or baculovirus-infected insect cells expressing individual PfEMP1

Methods

Results

Discussion

Conclusion