ABSTRACT
The Duffy binding-like (DBL) domain is a key adhesive module in Plasmodium falciparum, present in both erythrocyte invasion ligands (EBLs) and the large and diverse P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of cytoadherence receptors. DBL domains bind a variety of different host receptors, including intercellular adhesion molecule 1 (ICAM-1), a receptor interaction that may have a role in infected erythrocyte binding to cerebral blood vessels and cerebral malaria. In this study, we expressed the nearly full complement of DBLbeta-C2 domains from the IT4/25/5 (IT4) parasite isolate and showed that ICAM-1-binding domains (DBLbeta-C2(ICAM-1)) were confined to group B and group C PfEMP1 proteins and were not present in group A, suggesting that ICAM-1 selection pressure differs between PfEMP1 groups. To further dissect the molecular determinants of binding, we modelled a DBLbeta-C2(ICAM-1) domain on a solved DBL structure and created alanine substitution mutants in two DBLbeta-C2(ICAM-1) domains. This analysis indicates that the DBLbeta-C2::ICAM-1 interaction maps to the equivalent glycan binding region of EBLs, and suggests a general model for how DBL domains evolve under dual selection for host receptor binding and immune evasion.
Subject(s)
Antigens, Protozoan/metabolism , Host-Parasite Interactions , Intercellular Adhesion Molecule-1/metabolism , Plasmodium falciparum/metabolism , Protozoan Proteins/metabolism , Receptors, Cell Surface/metabolism , Amino Acid Sequence , Animals , Antigens, Protozoan/chemistry , Antigens, Protozoan/genetics , Binding Sites , COS Cells , Chlorocebus aethiops , Intercellular Adhesion Molecule-1/chemistry , Intercellular Adhesion Molecule-1/genetics , Models, Molecular , Molecular Sequence Data , Mutagenesis, Site-Directed , Phylogeny , Plasmodium falciparum/chemistry , Protein Binding , Protein Interaction Mapping , Protein Structure, Tertiary , Protozoan Proteins/chemistry , Protozoan Proteins/classification , Protozoan Proteins/genetics , Receptors, Cell Surface/chemistry , Receptors, Cell Surface/genetics , Sequence Alignment , Sequence AnalysisABSTRACT
Duffy-binding like (DBL) domains are common to two different families of malaria proteins that are involved in parasite invasion of erythrocytes or cytoadhesion of infected erythrocytes. DBL domain crystal structures have recently been solved for two different erythrocyte binding ligands, EBA-175 and the Plasmodium knowlesi alpha Duffy binding protein. These structures reveal different mechanisms for DBL binding and erythrocyte invasion. This review summarizes recent work on DBL domain binding and immune evasion and proposes a new structural model for how these domains adapted to intense antibody surveillance at the infected erythrocyte surface.
Subject(s)
Antigens, Protozoan/chemistry , Antigens, Protozoan/immunology , Cell Adhesion Molecules/chemistry , Cell Adhesion Molecules/immunology , Plasmodium falciparum/chemistry , Plasmodium falciparum/immunology , Protozoan Proteins/chemistry , Protozoan Proteins/immunology , Receptors, Cell Surface/chemistry , Receptors, Cell Surface/immunology , Amino Acid Sequence , Animals , Antigenic Variation , Antigens, Protozoan/genetics , Antigens, Protozoan/metabolism , Cell Adhesion Molecules/genetics , Cell Adhesion Molecules/metabolism , Erythrocytes/parasitology , Humans , Models, Molecular , Molecular Sequence Data , Plasmodium falciparum/metabolism , Protein Structure, Tertiary , Protozoan Proteins/genetics , Protozoan Proteins/metabolism , Receptors, Cell Surface/genetics , Receptors, Cell Surface/metabolism , Structure-Activity RelationshipABSTRACT
Genetic immunization is a novel method for vaccination in which DNA is delivered into the host to drive both cellular and humoral immune responses against its protein product. While genetic immunization can be potent, it requires that one have, in hand, a gene that encodes a protective protein antigen. Therefore, for many diseases, one cannot make a genetic vaccine because no protective antigen is known or no gene for this antigen is available. This lack of candidate antigens and their genes is a considerable bottleneck in developing new vaccines against old infectious agents, new emerging pathogens, and bioweapons. To address this limitation, we developed expression library immunization (ELI) as a high-throughput technology to discover vaccine candidate genes at will, by using the immune system to screen the entire genome of a pathogen for vaccine candidate. To date, ELI has discovered new vaccine candidates from a diverse set of bacterial, fungal, and parasitic pathogens. In addition, the process of applying ELI to the genome of pathogens allows one to genetically re-engineer these antigens to convert immunoevasive pathogen proteins into immunostimulatory vaccine antigens. Therefore, ELI is a potent technology to discover new vaccines and also generate genomic vaccines with amplified, multivalent immunostimulatory capacities.
