Host-Pathogen Interactions

The clinical symptoms of malaria occur upon host cell invasion by Plasmodium parasites, the causative agents of the disease. Therefore, recognition and invasion of host cells is an attractive target for therapeutics and an active area of research. Attachment of the parasite to a host cell during invasion requires specific receptor-ligand interactions. We aim to structurally and mechanistically define these interactions and attachment events. This knowledge is necessary to develop methods to inhibit invasion leading to therapeutic and vaccine design.

Project

CelTOS

To complete their life cycle, malaria parasites must move through various cells in the human and mosquito. Parasites that lack a protein called CelTOS can enter these cells, but remain stuck inside. We solved the structure of CelTOS to decipher its function and found CelTOS resembles pore-forming proteins. We futher demonstrated CelTOS forms pores in plasma membranes from the cytosolic face out to aid in parasite exit from cells.

John Jimah, Nichole D Salinas, Monica Sala-Rabanal, Nathaniel G Jones, L David Sibley, Colin G Nichols, Paul H Schlesinger, , "Malaria parasite CelTOS targets the inner leaflet of cell membranes for pore-dependent disruption." eLife (2016) Dec 1;5. pii: e20621. doi: 10.7554/eLife.20621.

Project

PfEBA-175 and Glycophorin A

The EBL family member erythrocyte binding antigen 175 (PfEBA-175) is a parasite surface protein and leading vaccine candidate for Plasmodium falciparum malaria. PfEBA-175 binds to the sugars of glycophorin A (GpA) on the red blood cell.

Nichole D Salinas#, May M Paing#, . "Critical glycosylated residues in exon three of erythrocyte glycophorin A engage Plasmodium falciparum EBA-175 and define receptor specificity." mBio (2014) 5(5):01606-14. doi:10.1128/mBio.01606-14.
# co-first author

Nichole D Salinas, . "A quantitative assay for binding and inhibition of Plasmodium falciparum Erythrocyte Binding Antigen 175 reveals high affinity binding depends on both DBL domains." Protein Expression and Purification (2014) pii: S1046-5928(13)00277-5. doi: 10.1016/j.pep.2013.12.008.

, Eric J Enemark, B Kim Lee Sim, Leemor Joshua-Tor. "Structural basis for the EBA-175 erythrocyte invasion pathway of the malaria parasite P. falciparum." Cell (2005) Jul 29; 122(2):183-93

Project

PvDBP and DARC

Plasmodium vivax is reliant on the Duffy Binding Protein (PvDBP) engagement of the Duffy Antigen/Receptor for Chemokines (DARC) on red blood cells for invasion. We have solved crystal structures of PvDBP in complex with DARC to identify the binding pockets. Our studies show that receptor binding drives dimerization of PvDBP, and PvDBP assembles around DARC for tight attachment.

Joseph D Batchelor, Brian M Malpede, Natalie S Omattage, Gregory T DeKoster, Katherine A Henzler-Wildman, . "Red Blood Cell Invasion by Plasmodium vivax: Structural Basis for DBP Engagement of DARC." PLOS Pathogens (2014) 10(1): e1003869. doi:10.1371/journal.ppat.1003869

Joseph D Batchelor, Jacob A Zahm, . "Dimerization of Plasmodium vivax DBP is induced upon receptor binding and drives recognition of DARC." Nature Structural & Molecular Biology (2011) Jul 10;18(8):908-14
Project

PfEBA-140 and Glycophorin C

Erythrocyte binding antigen 140 (PfEBA-140, BAEBL, EBL-2) is an EBL ligand that recognizes glycophorin C (GpC) on the red blood cell. The crystal and solution structure of PfEBA-140 shows distinct differences to PfEBA-175 that account for receptor specificity. The structure of PfEBA-140 in complex with glycans from the receptor Glycophorin C reveal novel glycan binding pockets different from other EBL ligands and sialic acid binding proteins. Polymorphisms in one of the glycan binding pockets may explain receptor switching by PfEBA-140.

Brian M Malpede, Daniel H Lin, . "Molecular Basis for Sialic Acid-dependent Receptor Recognition by Plasmodium falciparum Erythrocyte Binding Antigen 140/BAEBL." Journal of Biological Chemistry (2013) Apr 26;288(17):12406-15. Epub Mar 18.

Daniel H Lin, Brian M Malpede, Joseph D Batchelor, . "Crystal and Solution Structures of Plasmodium falciparum Erythrocyte Binding Antigen 140 Reveal Determinants of Receptor Specificity during Erythrocyte Invasion." Journal of Biological Chemistry (2012) Oct 26;287(44):36830-6. Epub Sep 18.

Neutralizing Antibodies

We are interested in understanding the molecular mechanisms of antibody-mediated neutralization. Several antibodies target the parasite proteins, but only a subset of the antibodies are neutralizing and can block invasion. Our work will determine the epitopes recognized by neutralizing antibodies, and characterize the mechanism of inhibition.

Project

Broadly neutralizing epitopes in PvDBP

Plasmodium vivax is reliant on the Duffy Binding Protein (PvDBP) engagement of the Duffy Antigen/Receptor for Chemokines (DARC) on red blood cells for invasion. We have identified inhibitory antibody epitopes that are conserved across global strains of PvDBP. These epitopes will inform future rounds of vaccine development.

Edwin Chen, Nichole D Salinas, Yining Huang, Francis B Ntumngia, Manolo D. Plascencia, Michael L. Gross, John H Adams, , "Broadly neutralizing epitopes in the Plasmodium vivax vaccine candidate Duffy Binding Protein." Proceedings of the National Academy of Sciences USA (2016) doi: 10.1073/pnas.1600488113.

Project

Antibodies that target PfEBA-175

A strongly-neutralizing antibody R217 (red) binds to the glycan-binding sites and proposed dimer interface of PfEBA-175. In contrast, a weakly neutralizing antibody R218 (green) binds to residues far removed from receptor-binding regions. This work suggests neutralizing antibodies target functional regions of invasion proteins.

Edwin Chen, May M. Paing, Nichole Salinas, B. Kim Lee Sim, . "Structural and Functional Basis for Inhibition of Erythrocyte Invasion by Antibodies that Target Plasmodium falciparum EBA-175." PLOS Pathogens (2013) 9(5): e1003390. doi:10.1371/journal.ppat.1003390

Aida S. Badiane, Amy K. Bei, Ambroise D. Ahouidi, Saurabh D. Patel, Nichole Salinas, Daouda Ndiaye, Ousmane Sarr, Omar Ndir, , Souleymane Mboup, and Manoj T. Duraisingh. "Inhibitory humoral responses to the Plasmodium falciparum vaccine candidate EBA-175 are independent of erythrocyte invasion pathway." Clinincal Vaccine Immunology (2013) 20(8):1238-45. doi: 10.1128/CVI.00135-13. Epub 2013 Jun 12.

Project

Antibody neutralization of PvDBP

Plasmodium vivax is reliant on the Duffy Binding Protein (PvDBP) engagement of the Duffy Antigen/Receptor for Chemokines (DARC) on red blood cells for invasion. Our studies show that receptor binding drives dimerization of PvDBP, and PvDBP assembles around DARC for tight attachment. This analysis also demonstrates that naturally acquired immunity targets the dimer interface and putative DARC binding site in PvDBP.

Joseph D Batchelor, Brian M Malpede, Natalie S Omattage, Gregory T DeKoster, Katherine A Henzler-Wildman, . "Red Blood Cell Invasion by Plasmodium vivax: Structural Basis for DBP Engagement of DARC." PLOS Pathogens (2014) 10(1): e1003869. doi:10.1371/journal.ppat.1003869

Joseph D Batchelor, Jacob A Zahm, . "Dimerization of Plasmodium vivax DBP is induced upon receptor binding and drives recognition of DARC." Nature Structural & Molecular Biology (2011) Jul 10;18(8):908-14

Antigen Engineering

Producing antigens that focus the immune response to protective epitopes is critical for future vaccines. We aim to design and engineer novel antigens that will lead to protection.

Project

Engineering PvDBP to focus the immune response

PvDBP is an excellent vaccine candidate for malaria. However, polymorphisms in PvDBP prevent strain specific responses reducing its efficacy as an antigen. Engineering PvDBP to eliminate strain-specific responses while boosting strain-transcengin protection is a major goal that will be achieved by structural vaccinology.

Edwin Chen, Nichole D Salinas, Francis B Ntumngia, John H Adams, , "Structural analysis of the synthetic Duffy Binding Protein (DBP) antigen DEKnull relevant for Plasmodium vivax malaria vaccine design." PLOS Neglected Tropical Diseases (2015) Mar 20;9(3):e0003644. doi: 10.1371/journal.pntd.0003644.

Antibiotic Resistance

The emergence of drug resistance to currently available anti-malarial and anti-bacterial drugs is a major challenge in control efforts. Therefore, defining the mechanisms that underlie drug resistance is of great importance. We will determine the molecular mechanisms that enable drug resistance through structural and mechanistic studies.

Project

Antibiotic resistance in bacteria

Tetracyclines are an important class of antibiotics whose use in the clinic and in agriculture have met with widespread resistance. By studying a novel family of tetracycline-inactivating enzymes from bacteria, we found diverse modes of antibiotic binding and catalysis, and defined the mechanism of catalysis that requires conformational changes in an FAD cofactor. Strikingly, we found that an inhibitor that locks the FAD conformation in an inactive state rescues tetracycline antibiotics. This novel insight enables a combination therapy to rescue tetracycline activity in the face of the emerging tetracycline inactive enzymes.

Jooyoung Park#, Andrew J Gasparrini#, Margaret R Reck, Chanez T Symister, Jennifer L Elliott, Joseph P Vogel, Timothy A Wencewicz*, Gautam Dantas*, *, "Plasticity, dynamics, and inhibition of emerging tetracycline resistance enzymes." Nature Chemical Biology (2017) Jul;13(7):730-736. doi: 10.1038/nchembio.2376.
# co-first author, * co-senior author

Project

Acquired drug resistance to fosmidomycin

Defining the structural and mechanistic basis for acquired drug resistance to the anti-malarial drug fosmidomycin. The structure of PfHAD1, an enzyme that modulates resistance to fosmidomycin.

Ann M Guggisberg#, Jooyoung Park#, Rachel L Edwards, Megan L Kelly, Dana M Hodge, *, Audrey R Odom*. "A sugar phosphatase regulates the methylerythritol phosphate (MEP) pathway in malaria parasites." Nature Communications (2014) 5:4467. doi: 10.1038/ncomms5467
# co-first author, * co-senior author


Project

Diverse substrate recognition by the drug resistance protein PfHAD1

PfHAD1 has a wide and diverse substrate specificity. We defined the structural basis for substrate ambiguity and specificity for this critical protein involved in drug resistance in malaria parasites.

Jooyoung Park#, Ann M Guggisberg#, Audrey R Odom*, *, "Cap-domain closure enables diverse substrate recognition by the C2-type haloacid dehalogenase-like sugar phosphatase Plasmodium falciparum HAD1." Acta Crystallographica Section D (2015) Sep;71(Pt 9):1824-34. doi: 10.1107/S1399004715012067.
# co-first author, * co-senior author