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Daniel E. Goldberg, M.D., Ph.D.
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Daniel E. Goldberg, M.D., Ph.D. Professor of Medicine and Molecular Microbiology & Co-Chair, Division of Infectious Diseases Research Chief, Division of Infectious Diseases Office Location: 9210 McDonnell Pediatric Research Building Dr. Goldberg joined the Division of Infectious Diseases in 1990. He received his M.D./Ph.D. degrees from Washington University, and did his internal medicine training at the Brigham and Women's Hospital in Boston. Dr. Goldberg trained in the infectious diseases fellowship program at Washington University School of Medicine, and joined the faculty after completing a post-doctoral fellowship at Rockefeller University in New York. The major focus of his research is on the biochemistry of malaria. Research Interests Intraerythrocytic malaria parasites degrade vast quantities of hemoglobin to provide nutrients for their growth and maturation. This process occurs in the acidic food vacuole. My laboratory is defining the proteolytic enzymes involved, their specificities and roles in hemoglobin breakdown, as well as their targeting to the food vacuole. The data suggest an ordered catabolic pathway. Four aspartic proteases (plasmepsins), a metalloprotease (falcilysin), three cysteine proteases (falcipains), a dipeptidyl peptidase (DPAP1) and aminopeptidases are involved in the process. The biosynthesis of the aspartic proteases appears to involve targeting to the parasite surface as integral membrane proenzymes and then ingestion with their substrate hemoglobin. Once the plasmepsin precursors reach the food vacuole, they are cleaved from the membrane by the falcipains at a conserved sequence at the plasmepsin pro-mature junction. The metalloprotease (falcilysin) cannot cleave hemoglobin or acid-denatured globin; rather it only works on fragmented globin or small, synthetic peptides. Falcilysin is capable of working at the acidic pH of the food vacuole. However, it also functions at neutral pH, where it has a very different substrate specificity. We have localized the enzyme to the apicoplast, where we believe it has a role in protein import. Further downstream in the hemoglobin degradation pathway, a dipeptidyl peptidase I of unusual specificity and multiple aminopeptidases have been isolated that appear to function in terminal degradation to liberate free amino acids. Gene knockout studies suggest that the downstream enzymes are essential, while the upstream enzymes (plasmepsins and falcipain-2) have considerable functional overlap. Parasites can be grown in culture medium containing isoleucine as the sole exogenous amino acid, demonstrating that P falciparum can use hemoglobin as its primary amino acid source. Under these conditions, knockout growth phenotypes are apparent. Once intraerythrocytic malaria parasites mature and replicate, they must exit the host cell to infect new erythrocytes. We have found that this is a two-step process. First, the parasites make a hole in the erythrocyte and escape bounded by their own parasitophorous vacuolar membrane. Then, the parasites must get out of this sac, which involves a specific proteolytic event. Further studies are focused on characterization of the implicated enzymes. Protease inhibitors block the escape and multiplication of the organism, suggesting that this is an attractive chemotherapeutic target. Our work involves a combination of biochemical, genetic, genomic and physiological approaches, to gain an understanding of the biology of this nefarious organism.
Division of Infectious Diseases
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