CRYSTAL STRUCTURE OF RNase-FORM I (COMPLEXED WITH NICKEL): Rama Balakrishnana, N. Ramasubbub*, K. I. Varughesec, R. Parthasarathy3, aCenter for Crystallographic Research and Biophysics Department, Roswell Park Cancer Institute, Buffalo, NY 14263, bResearch Center of Oral Biology, SUNY at Buffalo, Buffalo, NY 14214, cDepartment of Biology, University of California at San Diego, CA 92093.
The orthorhombic crystal form of Ribonuclease (Form I; King 1964) has been crystallized in the presence of six-fold excess of Nickel. The crystals belong to the space group P212121 with unit cell parameters a = 44.0, b = 75.5, c = 37.51Å, [[alpha]] = 90deg., [[beta]] = 90deg. and [[gamma]] = 90deg.. In 1956, Harker and coworkers (King et al 1956, 1962) showed that RNase could be crystallized in several forms indicating the versatility of packing of RNase molecules. Although a structure solution for these forms including form I was attempted earlier, only the monoclinic form (Form II) was successfully solved. We have initiated the structure solution of Form I because of our interest in Ni binding sites and the rarity of Ni in proteins. We have collected three-dimensional x-ray diffraction data of this crystal using the multiwire detector up to 2.6Å resolution (Cu K[[alpha]]). A total of 12,715 reflections were collected of which 12,103 are > 2s (Rsymm = 4.7%). The structure was solved by Molecular Replacement method using a phosphate-free RNase structure as starting model and using AmoRe and was refined using X-PLOR and PROLSQ to an R-factor of 20%. Further fitting of the electron density and refinement is in progress. Details of structure solution, refinement, and the effect of this metal on the structure will be investigated.
M. V. King, B. S. Magdoff, M. B. Adelman and D. Harker (1956), Acta Cryst., 9, 460 - 465.
M. V. King, J. Bello, E. H. Pignataro and D. Harker (1962), Acta Cryst, 15, 144 -147.
M. V. King (1964) Biochemica et Biophysica Acta, 79, 388-392.
*Supported by Grant DE08240 from USPHS