The Structure of Ribonuclease-S at 3.5 A Resolution

The electron density map of ribonuclease-S calculated from x-ray diffraction data on the protein and three heavy atom derivatives at 3.5 A resolution is interpretable in terms of main chain and side chain conformation with the aid of pre-existing chemical sequence data and general stereochemical knowledge. Stereoscopic pictures of part of the map and a skeletal model are presented. Features of the structure include 15% helix, 15% hydrophobic core, and appreciable antiparallel-β chain pairing. The configuration of the main chain and assignment of —S—S bridges closely resembles the structure of Rnase-A of Kartha, Bello, and Harker (3) except where there is a chemical difference. The structure is also compatible with much of the relevant chemical literature.