Crystallization and preliminary X-ray characterization of archaeal group II chaperonin alpha-subunit from Thermococcus strain KS-1.

Abstract

The archaeal group II chaperonin from Thermococcus strain KS-1 is composed of two kinds of subunits (alpha and beta). Each of the recombinant subunits was individually expressed in Escherichia coli and purified as homo-hexadecamers of each subunit. Both homo-oligomers facilitate the refolding of denatured proteins in vitro in an ATP-dependent manner. A mutant alpha-subunit homo-oligomer with two amino-acid substitutions, which has the ability to capture the unfolded protein but lacks the ability to refold the unfolded protein, was crystallized in two different conditions. One crystal form was obtained from a high-concentration solution of ammonium sulfate and grew to maximum dimensions of 0.15 x 0.15 x 0.4 mm. The crystals of this form belonged to the tetragonal space group P42(1)2, with unit-cell parameters a = b = 209.3, c = 156.1 A, and diffracted X-rays to 2.4 A resolution with synchrotron radiation. The other form was crystallized from a polyethylene glycol 6000 solution and belonged to the tetragonal space group, with unit-cell parameters a = b = 220.8, c = 182.4 A. This form only diffracts X-rays to 6 A resolution. Diffraction data collected from the former crystal enabled initial successful phases to be obtained by the molecular-replacement method.