The extracellular nuclease of Staphylococcus aureus: structures of the native enzyme and an enzyme-inhibitor complex at 4 A resolution.

Independent 4 A electron density maps calculated for the extracellular nuclease of Staphylococcus aureus (based on data from three heavy-atom derivatives) and for a nuclease-thymidine-3',5'-diphosphate-calcium ion complex (based on a single isomorphous derivative) show about 60 per cent of the chain resolved, including 3(1/2) turns of helix. The pyrimidine ring of the inhibitor fits into a pocket in the enzyme and appears to be parallel to the ring of a tyrosyl residue. Conformational changes can be observed between the nuclease and the nuclease-inhibitor complex, but the two structures seem to be identical over most of the molecule.