The crystal structure of the ImmE7
protein suggests a possible colicin-interacting surface.
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). |