Eukaryotic cells have developed sophisticated defenses aimed at limiting viral replication and thereby preventing infection from escalating to other cells. Among the many interferon-stimulated genes whose expression is up-regulated in the antiviral response is viperin (Virus Inhibitory Protein; Endoplasmic Reticulum associated, INterferon inducible), which has been shown to restrict the infectivity of a number of important human viruses including influenza A, HIV and hepatitis C. One of the most interesting features of viperin is that it appears to be a member of the radical SAM enzyme family; these enzymes reductively cleave S- adenosylmethionine to generate an adenosyl radical that is essential for catalysis. The involvement of radical SAM chemistry in the mammalian antiviral response was completely unexpected, as the radical SAM enzymes so far studied have almost exclusively been involved in microbial metabolism. Studies in mammalian cells have implicated a number of proteins, both cellular and viral, as targets of viperin. However, none of these interactions have been characterized directly and the mechanism(s) by which viperin inhibits its target enzymes, including the role of radical SAM chemistry in the reaction, remain unknown. We propose to study the interaction of viperin with farnesyl pyrophosphate synthase (FPPS), a key enzyme in the mevalonate biosynthetic pathway and the best-characterized target of viperin. Based on our preliminary data and well-documented protein modifications catalyzed by other radical SAM enzymes, we hypothesize that viperin inactivates FPPS by covalent modification, e.g. peptide-backbone cleavage, leading to its degradation. The project's goals are to determine the mechanism by which viperin inhibits FPPS, and then to extend these studies to other enzyme targets to establish whether viperin inhibits its targets by a common mechanism. The research will take a two-pronged approach that will combine studies on purified enzymes in vitro with studies on immuno-tagged enzymes transfected in mammalian cell lines. In vivo studies aim to evaluate the regulation of FPPS activity by viperin under physiological conditions. Targeted proteomics approaches will be used to identify other potential targets of viperin and to detect potential covalent modifications of FPPS by viperin in vivo. Targeted metabolomics approaches will be used to search for the products of radical SAM chemistry in vivo and to examine the perturbation of metabolites levels in the mevalonate pathway arising from inhibition of FPPS. In vitro studies will focus on determining in detail the mechanism by which viperin harnesses radical SAM chemistry to inactivate FPPS. Informed by the results of experiments on FPPS, the studies will be extended to examine the interaction of viperin with other target enzymes, including the mitochondrial trifunctional protein, which is involved in the catabolism of fatty acids by the -oxidation pathway.

Public Health Relevance

The project proposes to investigate how a cellular enzyme called viperin helps defend animals against viral infection. Viperin is has been shown to interact with both viral and other cellular enzymes, but how viperin inactivates these enzymes to prevent the virus replicating remains known. A better understanding of how this enzyme mediates the antiviral response may lead to more effective therapies for important viral diseases such as influenza, HIV and hepatitis C infections.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
2R01GM093088-05A1
Application #
8960243
Study Section
Macromolecular Structure and Function A Study Section (MSFA)
Program Officer
Anderson, Vernon
Project Start
2010-04-01
Project End
2019-03-31
Budget Start
2015-08-01
Budget End
2016-03-31
Support Year
5
Fiscal Year
2015
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Makins, Caitlyn; Ghosh, Soumi; Román-Meléndez, Gabriel D et al. (2016) Does Viperin Function as a Radical S-Adenosyl-l-methionine-dependent Enzyme in Regulating Farnesylpyrophosphate Synthase Expression and Activity? J Biol Chem 291:26806-26815
Marsh, E N G (2016) Whither Enzymology in the Twenty First Century? Front Chem 4:20
Funk, Michael A; Marsh, E Neil G; Drennan, Catherine L (2015) Substrate-bound structures of benzylsuccinate synthase reveal how toluene is activated in anaerobic hydrocarbon degradation. J Biol Chem 290:22398-408
Wang, Jiarui; Woldring, Rory P; Román-Meléndez, Gabriel D et al. (2014) Recent advances in radical SAM enzymology: new structures and mechanisms. ACS Chem Biol 9:1929-38
Waugh, Matthew W; Marsh, E Neil G (2014) Solvent isotope effects on alkane formation by cyanobacterial aldehyde deformylating oxygenase and their mechanistic implications. Biochemistry 53:5537-43
Funk, Michael A; Judd, Evan T; Marsh, E Neil G et al. (2014) Structures of benzylsuccinate synthase elucidate roles of accessory subunits in glycyl radical enzyme activation and activity. Proc Natl Acad Sci U S A 111:10161-6
Das, Debasis; Ellington, Benjamin; Paul, Bishwajit et al. (2014) Mechanistic insights from reaction of ?-oxiranyl-aldehydes with cyanobacterial aldehyde deformylating oxygenase. ACS Chem Biol 9:570-7
Buer, Benjamin C; Paul, Bishwajit; Das, Debasis et al. (2014) Insights into substrate and metal binding from the crystal structure of cyanobacterial aldehyde deformylating oxygenase with substrate bound. ACS Chem Biol 9:2584-93
Román-Meléndez, Gabriel D; von Glehn, Patrick; Harvey, Jeremy N et al. (2014) Role of active site residues in promoting cobalt-carbon bond homolysis in adenosylcobalamin-dependent mutases revealed through experiment and computation. Biochemistry 53:169-77
Paul, Bishwajit; Das, Debasis; Ellington, Benjamin et al. (2013) Probing the mechanism of cyanobacterial aldehyde decarbonylase using a cyclopropyl aldehyde. J Am Chem Soc 135:5234-7

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