SIMULTANEOUS REFINEMENT OF THE STRUCTURE OF BPTI AGAINST NMR DATA MEASURED IN SOLUTION AND X-RAY-DIFFRACTION DATA MEASURED IN SINGLE-CRYSTALS

The structure of the bovine pancreatic trypsin inhibitor (BPTI) has be en determined to high resolution by both NMR spectroscopy in solution and X-ray diffraction in crystals. The root-mean-square difference cal culated between the two structures for the polypeptide backbone is 0.9 Angstrom. Several amino acid side-chains, of which all but one are ch arged or polar, have different conformations. We find that by refining one structure simultaneously against both the NMR and crystallographi c data sets, it can accommodate both. Different starting configuration s were used, including the X-ray structure 5pti, an NMR conformer, and the X-ray structure in the full unit cell with extra solvent placed i n the bulk solvent region. The X-ray structures quickly converged to a ccommodate the NMR data in addition to the crystallographic data. Star ting from an NMR conformer, however, the convergence to accommodate th e more abundant X-ray data in addition to the NMR data is much slower.