title: The crystal structure of the immunity protein of colicin E7 suggests a possible colicin-interacting surface.
abstract: The immunity protein of colicin E7 (ImmE7) can bind specifically to the 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 alpha-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.
authors.affiliation: Institute of Biochemistry, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: K F
authors.initials: KF
authors.lastname: Chak
authors.forename: M K
authors.initials: MK
authors.lastname: Safo
authors.forename: W Y
authors.initials: WY
authors.lastname: Ku
authors.forename: S Y
authors.initials: SY
authors.lastname: Hsieh
authors.forename: H S
authors.initials: HS
authors.lastname: Yuan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D003087:Colicins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; C520411:ImmE7 protein, E coli; C007104:colicin immunity proteins