title: Allosteric Activation of SAMHD1 Protein by Deoxynucleotide Triphosphate (dNTP)-dependent Tetramerization Requires dNTP Concentrations That Are Similar to dNTP Concentrations Observed in Cycling T Cells.
abstract: SAMHD1 is a dNTP hydrolase, whose activity is required for maintaining low dNTP concentrations in non-cycling T cells, dendritic cells, and macrophages. SAMHD1-dependent dNTP depletion is thought to impair retroviral replication in these cells, but the relationship between the dNTPase activity and retroviral restriction is not fully understood. In this study, we investigate allosteric activation of SAMHD1 by deoxynucleotide-dependent tetramerization and measure how the lifetime of the enzymatically active tetramer is affected by different dNTP ligands bound in the allosteric site. The EC50dNTPvalues for SAMHD1 activation by dNTPs are in the 2-20 μm range, and the half-life of the assembled tetramer after deoxynucleotide depletion varies from minutes to hours depending on what dNTP is bound in the A2 allosteric site. Comparison of the wild-type SAMHD1 and the T592D mutant reveals that the phosphomimetic mutation affects the rates of tetramer dissociation, but has no effect on the equilibrium of allosteric activation by deoxynucleotides. Collectively, our data suggest that deoxynucleotide-dependent tetramerization contributes to regulation of deoxynucleotide levels in cycling cells, whereas in non-cycling cells restrictive to retroviral replication, SAMHD1 activation is likely to be achieved through a distinct mechanism.
authors: From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229 and.
authors: Zhonghua
authors: Z
authors: Wang
authors: From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229 and.
authors: Akash
authors: A
authors: Bhattacharya
authors: From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229 and.
authors: Jessica
authors: J
authors: Villacorta
authors: the Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461.
authors: Felipe
authors: F
authors: Diaz-Griffero
authors: From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229 and ivanov@uthscsa.edu.
authors: Dmitri N
authors: DN
authors: Ivanov
mesh_terms: D000494:Allosteric Regulation; D019943:Amino Acid Substitution; D003854:Deoxyribonucleotides / Q000737:chemistry* / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D055503:Protein Multimerization; D000076106:SAM Domain and HD Domain-Containing Protein 1; D013601:T-Lymphocytes / Q000201:enzymology
chemical_list: D003854:Deoxyribonucleotides; D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D020559:Monomeric GTP-Binding Proteins
keywords: autoimmune disease; human immunodeficiency virus (HIV); innate immunity; nucleoside/nucleotide metabolism; retrovirus