Kf. Chak et al., THE CRYSTAL-STRUCTURE OF THE IMMUNITY PROTEIN OF COLICIN E7 SUGGESTS A POSSIBLE COLICIN-INTERACTING SURFACE, Proceedings of the National Academy of Sciences of the United Statesof America, 93(13), 1996, pp. 6437-6442
The immunity protein of colicin E7 (ImmE7) can bind specifically to th
e DNase-type colicin E7 and inhibit its bactericidal activity, Here we
report the 1.8-Angstrom 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 alp
ha-helices, folded in a topology similar to the architecture of a four
-helix bundle structure, A region rich in acidic residues is identifie
d, This negatively charged area has the greatest variability within th
e family of DNase-type immunity proteins; thus, it seems likely that t
his area is involved in specific binding to colicin. Based on structur
al, genetic, and kinetic data, we suggest that all the DNase-type immu
nity proteins, as well as colicins, share a ''homologous-structural fr
amework'' and that specific interaction between a colicin and its cogn
ate immunity protein relies upon how well these two proteins' charged
residues match on the interaction surface, thus leading to specific im
munity of the colicin.