Interaction of Colicin E4 with Specific Receptor Sites Mediates Its Cleavage into Two Fragments Inactive Towards Whole Cells

Abstract

Colicin E4 has been iodinated with [125l]iodine. The relationship between the degree of iodination and the biological activity has been determined. In contrast to colicins E2, E3, Ia, Ib or cloacin, conventional saturation curves with sensitive cells are not obtained with colicin E4. A turnover ofcolicin on the receptors is evidenced. Analysis of the colicin molecules (Mr 56000 ± 2000) incubated in buffer with sensitive cells, on sodium dodecylsulfate/polyacrylamide gels shows that cleavage of the colicin molecules occurs to yield two fragments of 27000 Mr and 26000 Mr respectively. Strains selected for resistance to colicin E4 are defective in their ability to cleave this bacteriocin, whereas tolerant strains, which have an intact receptor but are not killed by colicin E4. cleave like sensitive cells. Colicin ‐ receptors interaction, which results in cleavage, is much less sensitive to the degree of iodination than the biological activity. Kinetics of cleavage as well as the effect of various treatments of sensitive cells are described. Among the various parameters which alter the cleavage, the most interesting is the ionic strength effect. In the presence of 0.5% or 1% NaCl, colicin E4 cleavage practically is not evidenced. We suggest that the equilibrium constant of the colicin‐receptor complex is very sensitive to ionic strength. The mechanism of colicin E4 cleavage with regard to the killing action is discussed. Copyright © 1979, Wiley Blackwell. All rights reserved