CRYSTALLIZATION AND PRELIMINARY-X-RAY INVESTIGATION OF BARSTAR, THE INTRACELLULAR INHIBITOR OF BARNASE

Crystals of barstar, the intracellular inhibitor of the extracellular ribonuclease produced by Bacillus amyloliquefaciens (barnase), were ob tained through vapor phase equilibration using the hanging drop techni que. Three crystal forms have been characterized. Forms I and II, crys tallized either in potassium phosphate or sodium citrate, are tetragon al; they exhibit a superstructure along the c-axis. Form III crystals, suitable for a high resolution structure determination, were grown fr om 55-65% ammonium sulfate. This crystal form is hexagonal and diffrac ts to at least 2 angstrom resolution at a synchrotron radiation source . It belongs to the hexagonal space group P6, with unit cell dimension s a = b = 143.6 angstrom, c = 35.6 angstrom. There are four molecules of barstar in the asymmetric unit. X-ray data have been collected to 2 .2 angstrom Bragg spacing. The structure determination is underway in order to analyze conformational changes of barstar upon complexation w ith barnase. (C) 1993 Wiley-Liss, Inc.