Nuclease activity of the human SAMHD1 protein implicated in the Aicardi-Goutieres syndrome and HIV-1 restriction.
The human HD domain protein SAMHD1 is implicated in the Aicardi-Goutières autoimmune syndrome and in the restriction of HIV-1 replication in myeloid cells. Recently, this protein has been shown to possess dNTP triphosphatase activity, which is proposed to inhibit HIV-1 replication and the autoimmune response by hydrolyzing cellular dNTPs. Here, we show that the purified full-length human SAMHD1 protein also possesses metal-dependent 3'→5' exonuclease activity against single-stranded DNAs and RNAs in vitro. In double-stranded substrates, this protein preferentially cleaved 3'-overhangs and RNA in blunt-ended DNA/RNA duplexes. Full-length SAMHD1 also exhibited strong DNA and RNA binding to substrates with complex secondary structures. Both nuclease and dNTP triphosphatase activities of SAMHD1 are associated with its HD domain, but the SAM domain is required for maximal activity and nucleic acid binding. The nuclease activity of SAMHD1 could represent an additional mechanism contributing to HIV-1 restriction and suppression of the autoimmune response through direct cleavage of viral and endogenous nucleic acids. In addition, we demonstrated the presence of dGTP triphosphohydrolase and nuclease activities in several microbial HD domain proteins, suggesting that these proteins might contribute to antiviral defense in prokaryotes.
Department of Chemical Engineering and Applied Chemistry, Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E5, Canada.
Natalia
N
Beloglazova
Department of Chemical Engineering and Applied Chemistry, Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E5, Canada.
Robert
R
Flick
Department of Chemical Engineering and Applied Chemistry, Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E5, Canada.
Anatoli
A
Tchigvintsev
Department of Chemical Engineering and Applied Chemistry, Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E5, Canada.
Greg
G
Brown
Department of Chemical Engineering and Applied Chemistry, Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E5, Canada.
Ana
A
Popovic
Bioscience Division, Argonne National Laboratory, Argonne, Illinois 60439.
Boguslaw
B
Nocek
Department of Chemical Engineering and Applied Chemistry, Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E5, Canada. Electronic address: a.iakounine@utoronto.ca.
Alexander F
AF
Yakunin
D019943:Amino Acid Substitution; D020274:Autoimmune Diseases of the Nervous System / Q000201:enzymology*; D020134:Catalytic Domain; D053837:DNA Cleavage; D004277:DNA, Single-Stranded / Q000737:chemistry; D005092:Exonucleases / Q000502:physiology*; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D006868:Hydrolysis; D008274:Magnesium / Q000737:chemistry; D058977:Molecular Sequence Annotation; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D009421:Nervous System Malformations / Q000201:enzymology*; D011485:Protein Binding; D012313:RNA / Q000737:chemistry; D059367:RNA Cleavage; D012367:RNA, Viral / Q000737:chemistry; D000076106:SAM Domain and HD Domain-Containing Protein 1; D014779:Virus Replication; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000235:genetics; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000235:genetics
D004277:DNA, Single-Stranded; D012367:RNA, Viral; D054301:gag Gene Products, Human Immunodeficiency Virus; D054322:tat Gene Products, Human Immunodeficiency Virus; D012313:RNA; D005092:Exonucleases; D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D020559:Monomeric GTP-Binding Proteins; D008274:Magnesium