SAMHD1, the Aicardi-Goutières syndrome gene and retroviral restriction factor, is a phosphorolytic ribonuclease rather than a hydrolytic ribonuclease

Ryoo, Jeongmin; Hwang, Sung-Yeon; Choi, Jong-Su; Oh, Changhoon; Ahn, Kwangseog

doi:10.1016/j.bbrc.2016.07.013

Cited by 21 publications

(27 citation statements)

References 31 publications

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“…Instead, PNPase activity is confined to a separate superfamily of proteins that are characterized by low K m values for the phosphate substrate (700 µM) and larger k cat values (~ 1 s −1 ) 53 . These kinetic parameters for a true PNPase are vastly superior to the previously reported PNPase activity of SAMHD1 19 . We conclude from the studies described here and previously that SAMHD1 has no detectable exonuclease or PNPase activities.…”

Section: Discussionmentioning

confidence: 50%

“…Moreover, a recent study has reported the detection of a polyribonucleotide phosphorylase activity of the enzyme in the presence of inorganic phosphate 19 . Although the ssNA binding site described above does not cluster near the known SAMD1 active site, which is consistent with our previous finding that SAMHD1 has neither nuclease or ribonuclease activity 17 , we felt compelled to investigate whether the newly proposed phosphorylase activity could be detected.…”

Section: Resultsmentioning

confidence: 99%

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Single-Stranded Nucleic Acids Bind to the Tetramer Interface of SAMHD1 and Prevent Formation of the Catalytic Homotetramer

2016

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Sterile Alpha Motif and HD Domain Protein 1 (SAMHD1) is a unique enzyme that has important roles in nucleic acid metabolism, viral restriction, and the pathogenesis of autoimmune diseases and cancer. Although much attention has been focused on its dNTP triphosphohydrolase activity in viral restriction and disease, SAMHD1 also binds to single-stranded RNA and DNA. Here we utilize a UV crosslinking method using 5-bromodeoxyuridine-substituted oligonucleotides coupled with high-resolution mass spectrometry (HRMS) to identify the binding site for single-stranded nucleic acids (ssNA) on SAMHD1. Mapping cross-linked amino acids on the surface of existing crystal structures demonstrated that the ssNA binding site lies largely along the dimer-dimer interface, sterically blocking the formation of the homotetramer required for dNTPase activity. Surprisingly, the disordered C-terminus of SAMHD1 (residues 583–626) was also implicated in ssNA binding. An interaction between this region and ssNA was confirmed in binding studies using the purified SAMHD1 583–626 peptide. Despite a recent report that SAMHD1 possesses polyribonucleotide phosphorylase activity, we did not detect any such activity in the presence of inorganic phosphate, indicating that nucleic acid binding is unrelated to this proposed activity. These data suggest an antagonistic regulatory mechanism where the mutually exclusive oligomeric state requirements for ssNA binding and dNTP hydrolase activity modulate these two functions of SAMHD1 within the cell.

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Section: Discussionmentioning

confidence: 50%

Section: Resultsmentioning

confidence: 99%

Single-Stranded Nucleic Acids Bind to the Tetramer Interface of SAMHD1 and Prevent Formation of the Catalytic Homotetramer

2016

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“…This was supported by a recent report that ribonuclease activity was not involved in SAMHD1‐mediated HIV‐1 restriction in cells . While these new findings seem to contradict the notion of antiviral RNase activity of SAMHD1, they have been rebutted, and the original RNase function of SAMHD1 has been defined to be a phosphorolytic ribonuclease rather than a hydrolytic ribonuclease . An attempt to reconcile the contradicting results was made explaining the differences with the different buffer systems used in the experiments.…”

Section: Does Samhd1 Have Antiviral Rnase Activity?mentioning

confidence: 70%

“…An attempt to reconcile the contradicting results was made explaining the differences with the different buffer systems used in the experiments. While the original observation was made using a phosphate buffer saline system to test nuclease activity, the contradicting study used a Tris‐base buffer system . Further work is needed because the most recent results from Seamon et al showed that SAMHD1 lacked polyribonucleotide phosphorylase activity in the presence of inorganic phosphate while Bloch et al found human SAMHD1 had no RNase activity and just one group reported the RNase function of SAMHD1 …”

Section: Does Samhd1 Have Antiviral Rnase Activity?mentioning

confidence: 99%

Roles of SAMHD1 in antiviral defense, autoimmunity and cancer

Zhang

Zhu

et al. 2017

Reviews in Medical Virology

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The enzyme, sterile α motif and histidine-aspartic acid domain-containing protein 1 (SAMHD1) diminishes infection of human immunodeficiency virus type 1 (HIV-1) by hydrolyzing intracellular deoxynucleotide triphosphates (dNTPs) in myeloid cells and resting CD4+ T cells. This dNTP degradation reduces the dNTP concentration to a level insufficient for viral cDNA synthesis, thereby inhibiting retroviral replication. This antiviral enzymatic activity can be inhibited by viral protein X (Vpx). The HIV-2/SIV Vpx causes degradation of SAMHD1, thus interfering with the SAMHD1-mediated restriction of retroviral replication. Recently, SAMHD1 has been suggested to restrict HIV-1 infection by directly digesting genomic HIV-1 RNA through a still controversial RNase activity. Here, we summarize the current knowledge about structure, antiviral mechanisms, intracellular localization, interferon-regulated expression of SAMHD1. We also describe SAMHD1-deficient animal models and an antiviral drug on the basis of disrupting proteasomal degradation of SAMHD1. In addition, the possible roles of SAMHD1 in regulating innate immune sensing, Aicardi-Goutières syndrome and cancer are discussed in this review.

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“…SAMHD1 has also been reported to exhibit exonuclease activity on ssRNA and ssDNA (86, 89, 90). The proposed mechanism of catalysis for SAMHD1 exonuclease activity is a phosphorolytic cleavage of the phosphodiester bond in nucleic acid polymers (91). These findings are widely contested however, as many groups report not being able to detect SAMHD1 nuclease activity or its effect on viral restriction (53, 83, 84, 92, 93).…”

Section: Samhd1 Activation Catalysis and Regulationmentioning

confidence: 99%

SAMHD1: Recurring roles in cell cycle, viral restriction, cancer, and innate immunity

Mauney

Hollis

2018

Autoimmunity

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SAMHD1 is a deoxynucleotide triphosphate (dNTP) hydrolase that plays an important role in the homeostatic balance of cellular dNTPs. Its emerging role as an effector of innate immunity is affirmed by mutations in the SAMHD1 gene that cause the severe autoimmune disease, Aicardi-Goutieres syndrome (AGS) and that are linked to cancer. Additionally, SAMHD1 functions as a restriction factor for retroviruses such as HIV. Here we review the current biochemical and biological properties of the enzyme including its structure, activity, and regulation by post-translational modifications in the context of its cellular function. We outline open questions regarding the biology of SAMHD1 whose answers will be important for understanding its function as a regulator of cell cycle progression, genomic integrity, and in autoimmunity.

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SAMHD1, the Aicardi-Goutières syndrome gene and retroviral restriction factor, is a phosphorolytic ribonuclease rather than a hydrolytic ribonuclease

Cited by 21 publications

References 31 publications

Single-Stranded Nucleic Acids Bind to the Tetramer Interface of SAMHD1 and Prevent Formation of the Catalytic Homotetramer

Single-Stranded Nucleic Acids Bind to the Tetramer Interface of SAMHD1 and Prevent Formation of the Catalytic Homotetramer

Roles of SAMHD1 in antiviral defense, autoimmunity and cancer

SAMHD1: Recurring roles in cell cycle, viral restriction, cancer, and innate immunity

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