Solubilization and Partial Characterization of the Colicin I Receptor of Escherichia coli

Treatment of the cell envelope of a colicin I-sensitive strain of Escherichia coli with the nonionic detergent Triton X-100 solubilizes an envelope component which forms a complex with 125I-colicin Ia and Ib. A similar component could not be shown in a strain known to be lacking active colicin I receptors. On this basis, this component is assumed to be the colicin I receptor. The colicin I receptor was found to be sensitive to trypsin, but insensitive to DNase, RNase, periodate, and phospholipases. Its capacity to bind colicin I was inhibited by salt. Sedimentation analysis in 5 to 20% sucrose gradients containing 0.05% Triton X-100 revealed that the colicin Iareceptor complex has a sedimentation constant of 12.4 S. Based on its behavior in gel filtration on Sepharose 6B columns containing detergent, the complex was shown to have a Stokes radius of 73.5 A. On the basis of these experiments, the colicin I-receptor complex has a molecular weight of 387,000 and a frictional ratio of about 1.5 and an axial ratio of about 8 or 9 for prolate or oblate ellipsoids, respectively.