Structures of SAMHD1 tetramers.

<p><b>(A</b>) Crystal structures of SAMHD1(41–583) (left) and SAMHD1(115–583) (right) tetramers. Individual monomers are coloured cyan, green, magenta and orange. Bound ddGTP molecules in the active and allosteric sites are shown in yellow and green stick representation respectively. Metal ions are shown as spheres. (<b>B</b>) The conserved dimer-dimer interface of SAMHD1(41–583) and SAMHD1(115–583) (left) and the non-conserved SAMHD1(115–583) dimer-dimer interface (right). For clarity only two SAMHD1 monomers, comprising one dimer-dimer interface are shown in each panel. Active site bound ddGTP and residues that make interactions at the subunit interface are shown as sticks. Dashed lines represent hydrogen bonding interactions. (<b>C</b>) A comparison of the bound nucleotide conformation and metal configuration of SAMHD1 tetramers is shown. Nucleotides are shown in stick representation, metal ions as spheres: Fe (brown), Mn (purple), Mg (green) and Zn (blue). SAMHD1 residues that chelate metal ions and/or triphosphate are labelled. (I) SAMHD1(41–583)-ddGTP, (II) SAMHD1(115–583)-ddGTP, (III) SAMHD1(113–626)-dGTPαS [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005194#ppat.1005194.ref013" target="_blank">13</a>] (PDB ID 4BZC), (IV) SAMHD1(113–626 HD206/207RN)-dGTP [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005194#ppat.1005194.ref013" target="_blank">13</a>] (PDB ID 4BZB), (V) SAMHD1(109–626)-dGTP [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005194#ppat.1005194.ref014" target="_blank">14</a>] (PDB ID 4MZ7).