CRYSTALLIZATION AND CHARACTERIZATION OF COLICIN E1 CHANNEL-FORMING POLYPEPTIDES

Crystals of the channel-forming domain of colicin E1 from E. coli were grown by vapor diffusion at pH 6.4 and higher pH values. Cleavage of the colicin molecule with trypsin or thermolysin produced two of the p ore-forming polypeptides used in these experiments. The third polypept ide was purified from a constructed plasmid that overexpresses only th e C-terminal domain of colicin E1. Polypeptide crystals are tetragonal with space group I4, have one monomer in the asymmetric unit, and dif fract to 2.2-2.4 Angstrom. Unit cell parameters for the tryptic and th ermolytic polypeptides are a = 102.9 Angstrom and c = 35.6 Angstrom. C rystals of the overexpressed polypeptide have unit cell parameters of a = 87.2 Angstrom and c = 59.1 Angstrom. The crystals were characteriz ed by precession photography, and native data sets of each channel-for ming fragment were collected on a Siemens-Nicolet area detector. The c rystallization and characterization of these polypeptides are the firs t steps in the structure determination of the channel-forming domain o f colicin E1. (C) 1994 Wiley-Liss, Inc.