Crystallization of the C-terminal domain of colicin A carrying the voltage-dependent pore activity of the protein.

The C-terminal fragment (Mr, 21,800) of colicin A (a bacterial toxin that kills sensitive Escherichia coli cells) has been crystallized. This fragment, which possesses the pore-forming activity of the toxin, resulted from thermolysin digestion of the entire molecule. The crystals are tetragonal, space group P4(1)2(1)2 (or P4(3)2(1)2) with a = b = 72.8 A, c = 170.4 A. They contain a dimer in the asymmetric unit and diffract to 2.7 A.