Abstract
To survive and replicate within the human host, malaria parasites must invade erythrocytes. Invasion can be mediated by the P. falciparum reticulocyte-binding homologue protein 4 (PfRh4) on the merozoite surface interacting with complement receptor type 1 (CR1, CD35) on the erythrocyte membrane. The PfRh4 attachment site lies within the three N-terminal complement control protein modules (CCPs 1-3) of CR1, which intriguingly also accommodate binding and regulatory sites for the key complement activation-specific proteolytic products, C3b and C4b. One of these regulatory activities is decay-accelerating activity. Although PfRh4 does not impact C3b/C4b binding, it does inhibit this convertase disassociating capability. Here, we have employed ELISA, co-immunoprecipitation, and surface plasmon resonance to demonstrate that CCP 1 contains all the critical residues for PfRh4 interaction. We fine mapped by homologous substitution mutagenesis the PfRh4-binding site on CCP 1 and visualized it with a solution structure of CCPs 1-3 derived by NMR and small angle x-ray scattering. We cross-validated these results by creating an artificial PfRh4-binding site through substitution of putative PfRh4-interacting residues from CCP 1 into their homologous positions within CCP 8; strikingly, this engineered binding site had an ∼30-fold higher affinity for PfRh4 than the native one in CCP 1. These experiments define a candidate site on CR1 by which P. falciparum merozoites gain access to human erythrocytes in a non-sialic acid-dependent pathway of merozoite invasion.
Highlights
Plasmodium falciparum merozoites invade erythrocytes via interaction of a pathogen protein PfRh4 with a host membrane receptor
We showed that the CR1/PfRh4 interaction is sensitive to high ionic strength, supporting the notion that electrostatic forces including salt bridges are crucial to receptor-ligand engagement. If these putative binding site residues are collectively substituted into their equivalent positions within CCP 8, the product is a version of LHR B that has a high affinity for PfRh4; this convincingly confirms our identification of the PfRh4-binding site in CCP 1 of CR1
Summary of statistics gathered for ensembles of CR1 1,2, CR1 2,3, and CR1 1–3
Summary
Plasmodium falciparum merozoites invade erythrocytes via interaction of a pathogen protein PfRh4 with a host membrane receptor. Binding Site of Malaria PfRh4 on Complement Receptor 1 junction forms between a merozoite and the erythrocyte membrane, which is triggered by and dependent on the initial receptor-parasite ligand interaction (5, 9). Chief among these parasite ligands are members of the erythrocyte-binding-like antigens (5, 10, 11) and the reticulocytebinding homologue proteins (PfRh) (5, 12, 13). We further identified key PfRh4-binding residues of CCP 1 using mutagenesis and placed them in a structural context by solving the three-dimensional structures of CCPs 1–3 These findings were further verified by the design and creation of a soluble engineered version of a CR1 fragment with a 30-fold enhanced affinity for PfRh4 that is a potential inhibitor of invasion. These studies will assist in the development of new therapeutic agents as well as strategies to prevent malaria
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
