Overview of the structure of S1 nuclease.

<p><b>(a)</b> S1 nuclease represented by its surface with important sites in sticks. The secondary structure representation is shown in the inset (helices are colored green, β–strands red, loops black). The catalytic zinc ions are shown as light blue spheres. Glycans are shown as sticks (carbon–green) and labelled according to the modified residues. Residues involved in the zinc cluster coordination are shown as sticks (carbon–green), residues forming NBS1, (also known as Phe–site) as sticks with carbon in yellow. Residues forming the Half–Tyr site are shown as sticks (carbon–magenta). NBS1 and the Half–Tyr site delimit the extent of the active site cleft. The graphics was created based on the structure 5FBF–nuclease products with removed 5’dCMP. <b>(b)</b> The active site of S1 nuclease. The color scheme is the same as in (a). Residues involved in the zinc cluster coordination and formation of NBS1 are labelled. The activated water molecule is labelled as W1, the water molecule present inside NBS1 as W_NBS1. Important interaction distances of W1, W_NBS1 and the distance of Asn154N^δ2 to Gly152O are given in Å. The graphics was created based on the structure 5FBA–phosphate, alternative without PO₄. Phe81 is shown in alternative A (occupancy factor 0.7). Molecular graphics were created using <i>PyMOL</i> (Schrödinger, LLC).