Does Viperin Function as a Radical S-Adenosyl-l-methionine-dependent Enzyme in Regulating Farnesylpyrophosphate Synthase Expression and Activity?
Viperin is an endoplasmic reticulum-associated antiviral responsive protein that is highly up-regulated in eukaryotic cells upon viral infection through both interferon-dependent and independent pathways. Viperin is predicted to be a radical S-adenosyl-l-methionine (SAM) enzyme, but it is unknown whether viperin actually exploits radical SAM chemistry to exert its antiviral activity. We have investigated the interaction of viperin with its most firmly established cellular target, farnesyl pyrophosphate synthase (FPPS). Numerous enveloped viruses utilize cholesterol-rich lipid rafts to bud from the host cell membrane, and it is thought that by inhibiting FPPS activity (and therefore cholesterol synthesis), viperin retards viral budding from infected cells. We demonstrate that, consistent with this hypothesis, overexpression of viperin in human embryonic kidney cells reduces the intracellular rate of accumulation of FPPS but does not inhibit or inactivate FPPS. The endoplasmic reticulum-localizing, N-terminal amphipathic helix of viperin is specifically required for viperin to reduce cellular FPPS levels. However, although viperin reductively cleaves SAM to form 5'-deoxyadenosine in a slow, uncoupled reaction characteristic of radical SAM enzymes, this cleavage reaction is independent of FPPS. Furthermore, mutation of key cysteinyl residues ligating the catalytic [Fe4S4] cluster in the radical SAM domain, surprisingly, does not abolish the inhibitory activity of viperin against FPPS; indeed, some mutations potentiate viperin activity. These observations imply that viperin does not act as a radical SAM enzyme in regulating FPPS.
From the Departments of Chemistry and.|Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055.
Caitlyn
C
Makins
From the Departments of Chemistry and.
Soumi
S
Ghosh
From the Departments of Chemistry and.
Gabriel D
GD
Román-Meléndez
From the Departments of Chemistry and.
Paige A
PA
Malec
From the Departments of Chemistry and.
Robert T
RT
Kennedy
From the Departments of Chemistry and nmarsh@umich.edu.|Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055.
E Neil G
EN
Marsh
D004721:Endoplasmic Reticulum / Q000378:metabolism*; D051228:Geranyltranstransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000737:chemistry* / Q000378:metabolism*; D000090123:Viperin Protein
D051228:Geranyltranstransferase; D050505:Mutant Proteins; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011506:Proteins; D012436:S-Adenosylmethionine; C444427:RSAD2 protein, human; D000090123:Viperin Protein
cholesterol; endoplasmic reticulum (ER); innate immunity; iron-sulfur protein; membrane enzyme; protein degradation; virus