title: Tetramerization of SAMHD1 is required for biological activity and inhibition of HIV infection.
abstract: SAMHD1 is a dGTP-activated dNTPase that has been implicated as a modulator of the innate immune response. In monocytes and their differentiated derivatives, as well as in quiescent cells, SAMHD1 strongly inhibits HIV-1 infection and, to a lesser extent, HIV-2 and simian immunodeficiency virus (SIV) because of their virion-associated virulence factor Vpx, which directs SAMHD1 for proteasomal degradation. Here, we used a combination of biochemical and virologic approaches to gain insights into the functional organization of human SAMHD1. We found that the catalytically active recombinant dNTPase is a dGTP-induced tetramer. Chemical cross-linking studies revealed SAMHD1 tetramers in human monocytic cells, in which it strongly restricts HIV-1 infection. The propensity of SAMHD1 to maintain the tetrameric state in vitro is regulated by its C terminus, located outside of the catalytic domain. Accordingly, we show that the C terminus is required for the full ability of SAMHD1 to deplete dNTP pools and to inhibit HIV-1 infection in U937 monocytes. Interestingly, the human SAMHD1 C terminus contains a docking site for HIV-2/SIVmac Vpx and is known to have evolved under positive selection. This evidence indicates that Vpx targets a functionally important element in SAMHD1. Together, our findings imply that SAMHD1 tetramers are the biologically active form of this dNTPase and provide new insights into the functional organization of SAMHD1.
authors: Department of Molecular Biology and Microbiology, Case Western Reserve School of Medicine, Cleveland, Ohio 44106, USA.
authors: Junpeng
authors: J
authors: Yan
authors: Sarabpreet
authors: S
authors: Kaur
authors: Maria
authors: M
authors: DeLucia
authors: Caili
authors: C
authors: Hao
authors: Jennifer
authors: J
authors: Mehrens
authors: Chuanping
authors: C
authors: Wang
authors: Marcin
authors: M
authors: Golczak
authors: Krzysztof
authors: K
authors: Palczewski
authors: Angela M
authors: AM
authors: Gronenborn
authors: Jinwoo
authors: J
authors: Ahn
authors: Jacek
authors: J
authors: Skowronski
mesh_terms: D015658:HIV Infections / Q000201:enzymology* / Q000235:genetics; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism*; D015498:HIV-2 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D000076106:SAM Domain and HD Domain-Containing Protein 1; D015302:Simian Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism; D020298:U937 Cells
chemical_list: D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D046988:Proteasome Endopeptidase Complex; D020559:Monomeric GTP-Binding Proteins