DETERMINATION OF THE 3-DIMENSIONAL SOLUTION STRUCTURE OF BARNASE USING NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The solution conformation of the ribonuclease barnase has been determined by using H-1 nuclear magnetic resonance (NMR) spectroscopy. The 20 structures were calculated by using 853 interproton distance restraints obtained from analyses of two-dimensional nuclear Overhauser spectra, 72-phi and 53-chi-1, torsion angle restraints, and 17 hydrogen-bond distance restraints. The calculated structures contain two alpha-helices (residues 6-18 and 26-34) and a five-stranded antiparallel beta-sheet (residues 50-55, 70-75, 85-91, 94-101, and 105-108). The core of the protein is formed by the packing of one of the alpha-helices (residues 6-18) onto the beta-sheet. The average RMS deviation between the calculated structures and the mean structure is 1.11 angstrom for the backbone atoms and 1.75 angstrom for all atoms. The protein is least well-defined in the N-terminal region and in three large loops. When these regions are excluded, the average RMS deviation between the calculated structures and the mean structure for residues 5-34, 50-56, 71-76, 85-109 is 0.62 angstrom for the backbone atoms and 1.0 angstrom for all atoms. The NMR-derived structure has been compared with the crystal structure of barnase [Mauguen et al. (1982) Nature (London) 297, 162-164].