Mapping the binding site of a cross-reactive Plasmodium falciparum PfEMP1 monoclonal antibody inhibitory of ICAM-1 binding

TY - JOUR

T1 - Mapping the binding site of a cross-reactive Plasmodium falciparum PfEMP1 monoclonal antibody inhibitory of ICAM-1 binding

AU - Lennartz, Frank

AU - Bengtsson, Anja

AU - Olsen, Rebecca W

AU - Joergensen, Louise

AU - Brown, Alan

AU - Remy, Louise

AU - Man, Petr

AU - Forest, Eric

AU - Barfod, Lea K

AU - Adams, Yvonne

AU - Higgins, Matthew K

AU - Jensen, Anja T R

N1 - Copyright © 2015 The Authors.

PY - 2015/10/1

Y1 - 2015/10/1

N2 - The virulence of Plasmodium falciparum is linked to the ability of infected erythrocytes (IE) to adhere to the vascular endothelium, mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1). In this article, we report the functional characterization of an mAb that recognizes a panel of PfEMP1s and inhibits ICAM-1 binding. The 24E9 mouse mAb was raised against PFD1235w DBLb3-D4, a domain from the group A PfEMP1s associated with severe malaria. 24E9 recognizes native PfEMP1 expressed on the IE surface and shows cross-reactivity with and cross-inhibition of the ICAM-1 binding capacity of domain cassette 4 PfEMP1s. 24E9 Fab fragments bind DBLb3-D4 with nanomolar affinity and inhibit ICAM-1 binding of domain cassette 4-expressing IE. The antigenic regions targeted by 24E9 Fab were identified by hydrogen/deuterium exchange mass spectrometry and revealed three discrete peptides that are solvent protected in the complex. When mapped onto a homology model of DBLb3-D4, these cluster to a defined, surface-exposed region on the convex surface of DBLb3-D4. Mutagenesis confirmed that the site most strongly protected is necessary for 24E9 binding, which is consistent with a low-resolution structure of the DBLb3-D4::24E9 Fab complex derived from small-angle x-ray scattering. The convex surface of DBLb3-D4 has previously been shown to contain the ICAM-1 binding site of DBLb domains, suggesting that the mAb acts by occluding the ICAM-1 binding surface. Conserved epitopes, such as those targeted by 24E9, are promising candidates for the inclusion in a vaccine interfering with ICAM-1-specific adhesion of group A PfEMP1 expressed by P. falciparum IE during severe malaria.

AB - The virulence of Plasmodium falciparum is linked to the ability of infected erythrocytes (IE) to adhere to the vascular endothelium, mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1). In this article, we report the functional characterization of an mAb that recognizes a panel of PfEMP1s and inhibits ICAM-1 binding. The 24E9 mouse mAb was raised against PFD1235w DBLb3-D4, a domain from the group A PfEMP1s associated with severe malaria. 24E9 recognizes native PfEMP1 expressed on the IE surface and shows cross-reactivity with and cross-inhibition of the ICAM-1 binding capacity of domain cassette 4 PfEMP1s. 24E9 Fab fragments bind DBLb3-D4 with nanomolar affinity and inhibit ICAM-1 binding of domain cassette 4-expressing IE. The antigenic regions targeted by 24E9 Fab were identified by hydrogen/deuterium exchange mass spectrometry and revealed three discrete peptides that are solvent protected in the complex. When mapped onto a homology model of DBLb3-D4, these cluster to a defined, surface-exposed region on the convex surface of DBLb3-D4. Mutagenesis confirmed that the site most strongly protected is necessary for 24E9 binding, which is consistent with a low-resolution structure of the DBLb3-D4::24E9 Fab complex derived from small-angle x-ray scattering. The convex surface of DBLb3-D4 has previously been shown to contain the ICAM-1 binding site of DBLb domains, suggesting that the mAb acts by occluding the ICAM-1 binding surface. Conserved epitopes, such as those targeted by 24E9, are promising candidates for the inclusion in a vaccine interfering with ICAM-1-specific adhesion of group A PfEMP1 expressed by P. falciparum IE during severe malaria.

M3 - Journal article

C2 - 26320251

SN - 0022-1767

VL - 195

SP - 3273

EP - 3283

JO - Journal of Immunology

JF - Journal of Immunology

IS - 7

ER -