Structural characterization of host-pathogen interactions

National Institute Of Allergy And Infectious Diseases

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Abstract

There is a fundamental lack of knowledge of the modalities and principles that govern pathogen-host interactions preventing rational design of approaches to effectively disrupt such interactions to achieve efficient pathogen control. In the past, simple models of monomeric binding for receptor-ligand interactions have been invoked simplifying experimental study but limiting our understanding of how interactions are truly manifested during pathogenesis. Recently, the larger view of interactions suggests that the induction of multimeric assemblies and higher order states upon binding, through oligomerization or tandem duplication of binding sites, are critical to the formation of strong interactions between the parasite and the host/vector. The identification of all multimeric contact interfaces within a complex, including interaction and oligomerization contacts, is not only fundamental to the structural understanding of interactions but also reveals additional targets for disruption as described below. We plan to comprehensively dissect the fundamental principles that drive the multimeric assembly of pathogen-host interactions, and that enable their efficient disruption at the molecular level. We focus on essential host-pathogen/receptor-ligand interactions required for host infection and vector transmission of the malaria parasites Plasmodium falciparum and Plasmodium vivax. The fundamental principles of this study include multimerization of interacting partners, creation of specific binding pockets, and characterization of structural changes upon binding, as well as the role of multiple binding sites within a complex with respect to cooperativity and avidity. The role of variable (polymorphic) and constant regions of interacting partners in engagement will also be uncovered. These fundamental principles will be revealed by studying the structural and mechanistic basis for the assembly of parasite-host interaction, with well-validated roles as potential vaccine candidates and/or as required for parasite viability. In FY25, we continued our efforts to obtain full-length host-pathogen receptor-ligand structures of multiple key parasite proteins. We focused on the MSP1 multiprotein complex, the AMA1-RON complex and the EBL family proteins in complex with host receptors as all complexes are crucial for parasite invasion of the human host. We have made progress on the production and stabilization of the complexes suitable for structural study through both cryogenic electronic microscopy and X-ray crystallography. The structural efforts are complemented by extensive biophysical interaction studies to establish mass, stoichiometry, affinity and kinetic binding parameters for the complexes. These findings will aid in the development of interventions for malaria, inform fundamental principle of receptor-ligand interactions and inform parasite biology. In collaboration with Elizabeth Egan’s group (Stanford University), we continue to investigate the role of the host-receptor CD44 in parasite invasion. Our prior work contributing to identifying CD44 as a co-receptor for the EBL family of parasites has formed a strong foundation to determine the role of CD44 binding in inducing cellular changes in the parasite, and in clustering of red cells that we have shown can enhance parasite growth and protect from neutralizing antibodies. We continue to pursue investigation of CD44 toward uncovering the molecular role and structural basis for the interaction with the parasite. In collaboration with David Serre’s group (University of Maryland), we are investigating Plasmodium vivax surface proteins. Plasmodium vivax blood-stage parasites have a surface proteome distinct from Plasmodium falciparum and less is known about these proteins. We have screened a large panel of these surface proteins and identified approximately 15 biologically and immunologically important proteins. These proteins have been purified for upcoming studies of their roles and interactions with the human host.