W0306

Neutron Diffraction Analysis of Rubredoxin from Pyrococcus Furiosus at 1.5 Å Resolution. Robert Bau, Chemistry Dept., Univ. of Southern California, Los Angeles, CA 90089.

Single-crystal neutron diffraction data up to a resolution of 1.5 Å have been collected at room temperature on two forms of rubredoxin using the BIX-3 diffractometer at the JRR-3 reactor of JAERI (the Japan Atomic Energy Research Institute). Rubredoxin is a small iron-sulfur redox protein with 53 amino acid residues, and the source of this particular protein is the hyperthermophile Pyrococcus furiosus, a microorganism that normally lives at temperatures near that of boiling water. Data were collected on crystals of the wild-type protein and on a mutant in which three of the residues have been replaced. We were originally interested to see if the results of the neutron analysis would provide some reasons to explain the remarkable thermal stability of the wild-type protein from this intriguing microorganism. In this talk we will be discussing several sets of results arising from these high-resolution neutron structure determinations: (a) the H/D exchange pattern of the N-H bonds of the main backbone, which give information about which regions of the molecule are more exposed to solvent; (b) the structure and appearance of water molecules in the protein crystals; (c) the orientations of some of the O-D bonds in the protein, information which is often not obtainable from X-ray results; and (d) the differences in the hydrogen-bonding patterns between the wild-type protein and the triple mutant, which might rationalize the thermostability differences between these two different rubredoxins.