The HIV-1 restriction factor SAMHD1 is a tetrameric enzyme activated by

The HIV-1 restriction factor SAMHD1 is a tetrameric enzyme activated by guanine nucleotides with dNTP triphosphate hydrolase activity (dNTPase). in vivo model is usually suggested where SAMHD1 Rabbit Polyclonal to MMP-3 alternates between the mutually exclusive functions of ssRNA binding and dNTP hydrolysis depending on dNTP pool levels and the presence of viral ssRNA. It is quite common that enzymes with one major activity also catalyze other minor reactions that make use of the same energetic site environment and catalytic residues (1,2). One traditional example may be the main DNA phosphodiester hydrolysis activity of DNase I and its own minimal activity of 3-phosphate monoester hydrolysis Amentoflavone manufacture from DNA ends (3,4). Both reactions take place in the same energetic site and make use of the equivalent energetic site components most likely, despite the fact that the changeover expresses and catalytic requirements for hydrolysis of phosphate monoesters and diesters are very different (5,6). Thus, generally it isn’t unanticipated that dNTP hydrolases may also possess other phosphate ester hydrolyzing activities and that these additional activities might be of biological significance. Sterile Alpha Motif and Histidine-Aspartate Domain name 1 protein (SAMHD1) is usually a Mg2+-dependent homotetrameric enzyme that indiscriminately hydrolyzes all dNTPs to deoxynucleoside and tripolyphosphate products (7,8). The enzyme plays a key role in an innate immunity pathway that restricts HIV-1 contamination of resting immune cells by preventing efficient completion of reverse transcription. The mechanism may involve depletion of the dNTP substrates of reverse transcriptase and/or other activities of SAMHD1 (9). SAMHD1 also contributes to the stability of the genome by Amentoflavone manufacture restricting the replication of mutagenic retroelements, although this function does not appear to require its dNTPase activity (10). Mutations at the SAMHD1 locus are associated with the inherited inflammatory autoimmune disease Aicardi-Goutires syndrome that mimics chronic viral contamination (11). SAMHD1 has a complex activation mechanism including nucleotide Amentoflavone manufacture binding to two classes of activator sites (A1 and A2) as well as four catalytic sites around the HD domain name of each tetramer. Nucleotide binding energy is used to induce oligomerization of the enzyme from its inactive monomer and dimer forms that predominate in the absence of nucleotide activation (12,13). Nucleotide activation has been shown to follow an ordered-essential mechanism (14): preferential Amentoflavone manufacture binding of GTP to the Amentoflavone manufacture four A1 sites promotes dimerization, which is usually followed by binding of any dNTP to each of four A2 sites, and substrate dNTPs to each of the four catalytic sites. Occupation of all the sites is required to drive the dimer to tetramer transition. Thus, amazingly, the SAMHD1 tetramer binds a total of twelve nucleotides in its triggered state, and the tetramer is definitely stable for many hours after nucleotides have been depleted (14). The enzyme is definitely evolutionarily related to a large superfamily of HD-domain proteins that contain a characteristic H…HDD sequence motif required for divalent metallic ion binding (15). Although the vast majority of the known HD family members have phosphohydrolase activities, recent studies possess uncovered a clade that possesses mixed-valent diirion-dependent oxygenase activity (16,17). Therefore, the architecture of this protein fold and its metallic binding properties are capable of yielding varied enzymatic catalytic properties. Although several organizations possess verified that SAMHD1 binds ssDNA and ssRNA qualitatively, however, not duplex DNA or duplex RNA/DNA hybrids (18C20), there were conflicting and multiple reviews concerning whether SAMHD1 provides 3-5 exonuclease activity (7,18,19,21). Notably, Beloglazova RNA exonuclease activity, that have been expanded to cell structured research that indicated the RNase activity was needed for.