Sean Prigge - US grants

Amidated peptides are fundamental signaling molecules found in species ranging from Aplysia to humans. Surprisingly, peptide amidation is not carried out by a transamination reaction, but by oxidative cleavage, glycine-extended precursors. A bifunctional enzyme, peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes this reaction. The PAM gene encodes two domains (PHM and PAL) that catalyze two sequential reactions: alpha-hydroxylation of the glycine (PHM) and excision of the C alpha-N bond to give alpha-amidated peptide (PAL). PHM contains two redox active copper atoms that, upon reduction by ascorbate, catalyze the reduction of molecular oxygen for the hydroxylation of glycine-extended substrates. PAL is a zinc containing lyase that cleaves the C alpha-N bond after hydroxylation of the C alpha. This project will employ X-ray diffraction, kinetic experiments, peptide design, and site directed mutagenesis to elucidate important aspects of the mechanism of reactions catalyzed by PHM and PAL. Understanding the chemistry of PAM, especially that of the first step of the reaction, will not only contribute to the field of peptide amidation, but will also provide an outstanding paradigm for understanding long range electron transfer and the prevention of production of deleterious oxygen species.

Broader Impacts: The PI of this project is actively involved in teaching as well as in bringing the excitement of science to underrepresented minorities. Mentoring of minority students will be achieved through participation in the Meyerhoff Scholars Programs of the University of Maryland Baltimore Campus. The project will also involve participation in the Science Day organized in conjunction with the Baltimore City school system.

[unreadable] DESCRIPTION (provided by applicant): Malaria parasites are responsible for 300-500 million infections and 2-3 million deaths annually. During the asexual stages of development in red blood cells, parasites acquire certain nutrients from human serum while retaining the ability to synthesize others. We are studying an essential enzyme cofactor called lipoate and its metabolism in Plasmodium falciparum. Our recent studies indicate that malaria parasites contain a metabolic pathway to synthesize lipoate de novo from intermediates of fatty acid biosynthesis as well as two mechanisms for scavenging lipoate from human serum. These pathways appear to reside in different subcellular compartments in the parasite and may be independent and essential for parasite survival. The proposed studies will employ biochemical, cell biology and genetic approaches to investigate these unexplored pathways and establish the roles of synthesized and host-derived lipoate in parasite survival. Specific Aim 1 will define the activities and organization of the P. falciparum lipoate biosynthetic machinery and the role of synthesized lipoate in parasite survival. Specific Aim 2 will define the role of exogenous lipoate in parasite survival, its distribution in the parasite, and the activities and organization of the P. falciparum lipoate scavenging pathways. These studies could establish the existence of an intracellular metabolite trafficking pathway between the apicoplast organelle and the mitochondrion of malaria parasites. Alternatively, these studies could demonstrate that P. falciparum parasites are auxotrophic for lipoate despite the existence of a lipoate biosynthetic pathway. Proteins responsible for the metabolism of lipoate may ultimately prove to be attractive targets for therapeutic intervention - especially since inhibitors could act synergistically with known inhibitors of P. falciparum fatty acid biosynthesis. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Continued training in The Molecular and Cellular Bases of Infectious Diseases (MCBID) is proposed for 8 PhD students and 3 postdoctoral fellows selected from large pools of highly qualified applicants. The training program is uniquely situated in the Molecular Microbiology and Immunology Department (MMI) within the Johns Hopkins Bloomberg School of Public Health. The 29 training faculty have a wide range of experience and expertise in viruses, bacteria and parasites causing human disease and in the vectors and environmental factors associated with emergence and transmission of these pathogens. The training program has been funded since 1994 and has produced scientists working in many areas of academia and government on problems related to infectious diseases, vaccine development and the public's health. The goal of the MCBID training program is to provide students with both a firm foundation in the basic disciplines necessary for the study of infectious diseases and a perspective that will enable them to apply their knowledge creatively to public health problems. Each student is expected to complete 1) a series of required courses in the basic disciplines of cell and molecular biology, biochemistry, and immunology, 2) courses in virology, bacteriology, parasitology, and disease ecology, 3) courses in research ethics and public health perspectives, and 4) elective courses relevant to thesis topic and long-term career goals. Elective courses are chosen from among courses available in MMI, other departments in the School of Public Health, or in other Divisions of the University. Students will also complete 3 11-week laboratory rotations during the first year. Student progress is monitored by a Thesis Advisory Committee and the Graduate Program Committee. The goals of the postdoctoral training program are 1) to provide focused training in those areas of the molecular and cellular basis of infectious diseases in which program faculty have special expertise;2) to provide an opportunity for doctoral degree holders trained in more traditional environments to broaden their exposure to problems of public health importance and to evaluate their career goals in terms of public health issues;and 3) to prepare the PDF for an independent career in the biological sciences. RELEVANCE : This program is highly relevant to national interests in the areas of emerging infectious diseases, as it trains students and postdoctoral fellows broadly not only in both the molecular aspects of pathogen biology and disease pathogenesis, but also in the ecology of disease emergence and the role of vectors in pathogen transmission.

DESCRIPTION (provided by applicant): Genetic methods to control protein levels are extremely valuable tools for probing the basic biology of any organism. Two commonly employed tools are RNA interference and conditional expression, neither of which has been successfully implemented in malaria research. We are developing a new method to control proteins in the secretory pathway of malaria parasites. Over 20% of the proteins encoded by the Plasmodium falciparum genome are thought to pass through the secretory system on their way to organellar or extracellular destinations. These proteins have key roles in parasite metabolism, nutrient acquisition, invasion, host cell remodeling, and other critical aspects of parasite biolog. The goal of this project is to design and optimize a conditional probe to control the localization f soluble secretory proteins in P. falciparum. This method will then be validated by applying it to two biological targets: one in the apicoplast organelle and one which resides in the parasitophorous vacuole. Successful development of a conditional localization tool will enhance our ability to probe the basic biology of malaria parasites and will allow us to validate potential targets for therapeutic intervention. PUBLIC HEALTH RELEVANCE: The inevitable rise of drug-resistant malaria parasites creates a continuing need to develop new control strategies. We are developing a genetic tool that will help to probe basic parasite biology and validate new drug targets.

DESCRIPTION (provided by applicant): Continued training in The Molecular and Cellular Bases of Infectious Diseases (MCBID) is proposed for 8 PhD students and 3 postdoctoral fellows selected from large pools of highly qualified applicants. The training program is uniquely situated in the Molecular Microbiology and Immunology Department (MMI) within the Johns Hopkins Bloomberg School of Public Health. The 29 training faculty have a wide range of experience and expertise in viruses, bacteria and parasites causing human disease and in the vectors and environmental factors associated with emergence and transmission of these pathogens. The training program has been funded since 1994 and has produced scientists working in many areas of academia and government on problems related to infectious diseases, vaccine development and the public's health. The goal of the MCBID training program is to provide students with both a firm foundation in the basic disciplines necessary for the study of infectious diseases and a perspective that will enable them to apply their knowledge creatively to public health problems. Each student is expected to complete 1) a series of required courses in the basic disciplines of cell and molecular biology, biochemistry, and immunology, 2) courses in virology, bacteriology, parasitology, and disease ecology, 3) courses in research ethics and public health perspectives, and 4) elective courses relevant to thesis topic and long-term career goals. Elective courses are chosen from among courses available in MMI, other departments in the School of Public Health, or in other Divisions of the University. Students will also complete 3 11-week laboratory rotations during the first year. Student progress is monitored by a Thesis Advisory Committee and the Graduate Program Committee. The goals of the postdoctoral training program are 1) to provide focused training in those areas of the molecular and cellular basis of infectious diseases in which program faculty have special expertise; 2) to provide an opportunity for doctoral degree holders trained in more traditional environments to broaden their exposure to problems of public health importance and to evaluate their career goals in terms of public health issues; and 3) to prepare the PDF for an independent career in the biological sciences. RELEVANCE : This program is highly relevant to national interests in the areas of emerging infectious diseases, as it trains students and postdoctoral fellows broadly not only in both the molecular aspects of pathogen biology and disease pathogenesis, but also in the ecology of disease emergence and the role of vectors in pathogen transmission.

Malaria parasites contain a plastid organelle called the apicoplast that is required for parasite survival in humans and for transmission to mosquitoes. The apicoplast has long been recognized as an important source of new drug targets to combat the inevitable problem of drug resistance, however, it has proven difficult to identify and validate apicoplast proteins that are essential for parasite survival. This goal is now achievable using new genetic tools in combination with metabolic bypass of the apicoplast. Blood stage parasites treated with the isoprene compound IPP (isopentenyl pyrophosphate) survive apicoplast inhibitors - even those which result in disruption of the organelle and loss of the organellar genome. Recently, we used the IPP metabolic bypass to demonstrate that iron-sulfur cluster biosynthesis is essential for maintenance of the organelle. We propose to use reverse and forward genetic approaches in conjunction with metabolic bypass to identify other nuclear-encoded proteins which are essential for apicoplast function and parasite survival. We will also use a new conditional localization tool to further characterize the roles of specific proteins and the phenotypes associated with their loss. Our experiments will help to build a more complete picture of the metabolic pathways and non-metabolic processes required for apicoplast function and parasite survival. Ultimately, we intend to identify novel targets and to validate known targets for future development of drugs to cure malaria and stop its transmission.

Malaria parasites contain a plastid organelle called the apicoplast that is required for parasite survival in humans and for transmission to mosquitoes. The apicoplast has long been recognized as an important source of new drug targets to combat the inevitable problem of drug resistance, however, it has proven difficult to identify and validate apicoplast proteins that are essential for parasite survival. This goal is now achievable using new genetic tools in combination with metabolic bypass of the apicoplast. Blood stage parasites treated with the isoprene compound IPP (isopentenyl pyrophosphate) survive apicoplast inhibitors - even those which result in disruption of the organelle and loss of the organellar genome. Recently, we used the IPP metabolic bypass to demonstrate that iron-sulfur cluster biosynthesis is essential for maintenance of the organelle. We propose to use reverse and forward genetic approaches in conjunction with metabolic bypass to identify other nuclear-encoded proteins which are essential for apicoplast function and parasite survival. We will also use a new conditional localization tool to further characterize the roles of specific proteins and the phenotypes associated with their loss. Our experiments will help to build a more complete picture of the metabolic pathways and non-metabolic processes required for apicoplast function and parasite survival. Ultimately, we intend to identify novel targets and to validate known targets for future development of drugs to cure malaria and stop its transmission.