Date of Award
Doctor of Philosophy (PhD)
The malaria parasite Plasmodium utilizes specialized proteins for adherence to cellular receptors in its mosquito vector and human host. Adherence is critical for parasite development, host cell traversal and invasion, and protection from vector and host immune mechanisms. These vital roles have identified several adhesins as vaccine candidates. A deficiency in current adhesin-based vaccines is induction of antibodies targeting non-conserved, non-functional, and decoy epitopes due to the use of full length proteins or binding domains. To alleviate the elicitation of non-inhibitory antibodies, conserved functional regions of proteins must be identified and exploited. Structural biology provides the tools necessary to achieve this goal, and has succeeded in defining biologically functional receptor binding and oligomerization interfaces for a number of promising malaria vaccine candidates.
A critical step in the Plasmodium life cycle is adhesion to and invasion of erythrocytes by the merozoite during blood stage growth. The invasion process requires the formation of a tight junction between parasite adhesive proteins and red cell receptors. Formation of this junction allows the merozoite to engage and enter the red cell to form the parasitophorous vacuole. The
Erythrocyte-binding-like (EBL) family of cellular adhesion proteins is implicated in the formation of this essential tight junction.
Receptor binding by the EBL family of invasion ligands has been localized to a specific portion of each EBL protein designated Region II (RII). This region is composed of the Duffy- binding-like (DBL) domain, unique to Plasmodium species. The two Plasmodium species responsible for the majority of malaria disease in humans are P. falciparum and P. vivax. There are four identified EBL members in P. falciparum that contain two tandem DBL domains in RII. This organization contrasts the single DBL domain in RII of the only characterized EBL member of P. vivax, Duffy-binding Protein (PvDBP). Using a combination of structural, biophysical, and cellular interaction methods we examined the binding mode for these two Plasmodium EBL family members to define the molecular and mechanistic basis of unique red cell invasion routes.
Specifically, we sought to enhance our understanding of the molecular and mechanistic details of invasion by Plasmodium EBL ligands with the ultimate goal of identifying novel targets for rational vaccination efforts. We examined receptor interactions of a P. falciparum EBL member, Erythrocyte-binding-antigen 140 (PfEBA-140) and P. vivax DBP to provide insight into invasion by both species of parasite. Our work identified unique interfaces on the DBL domain that provide specific recognition of each ligand's unique red blood cell receptor. Additionally, studies examining oligomeric state identified distinct mechanistic parameters for the two EBL ligands, and contrasted with the mechanism observed for another P. falciparum member, PfEBA-175.
Chair and Committee
Niraj H Tolia
Gaya Amarasinghe, Deepta Bhattacharya, Daved Fremont, Dan Goldberg, Audrey Odom, David Sibley
Malpede, Brian Michael, "Molecular Mechanisms of Plasmodium Red Blood Cell Invasion" (2015). Arts & Sciences Electronic Theses and Dissertations. 456.