Chak, K.-F., Safo, M. K., Ku, W.-Y., Hsieh, S.-Y., and Yuan, H. S.

Abstract

      The immunity protein of colicin E7 (ImmE7) can bind specifically to the  DNase-type colicin E7 (ColE7) and inhibit its bactericidal activity.  Here we report the 1.8 ?crystal structure of the ImmE7 protein.  This is the first X-ray structure determined in the superfamily of colicin immunity proteins.  The ImmE7 protein consists of four antiparallel a-helices, folded in a topology similar to the architecture of a four-helix bundle structure.  A region rich in acidic residues is identified.  This negatively charged area has the greatest variability within the family of DNase-type immunity proteins; thus it seems likely that this area is involved in specific binding to colicin.  Based on structural, genetic and kinetic data, we suggest that all the DNase-type immunity proteins, as well as colicins, share a "homologous-structural framework" and that specific interaction between a colicin and its cognate immunity protein relies upon how well these two proteins' charged residues match on the interaction surface, thus leading to specific immunity of the colicin.

Proc. Natl. Acad. Sci. USA, 93, 6437-6442 (1996).