title: High-resolution crystal structure of a truncated ColE7 translocation domain: implications for colicin transport across membranes.
abstract: ColE7 is a nuclease-type colicin released from Escherichia coli to kill sensitive bacterial cells by degrading the nucleic acid molecules in their cytoplasm. ColE7 is classified as one of the group A colicins, since the N-terminal translocation domain (T-domain) of the nuclease-type colicins interact with specific membrane-bound or periplasmic Tol proteins during protein import. Here, we show that if the N-terminal tail of ColE7 is deleted, ColE7 (residues 63-576) loses its bactericidal activity against E.coli. Moreover, TolB protein interacts directly with the T-domain of ColE7 (residues 1-316), but not with the N-terminal deleted T-domain (residues 60-316), as detected by co-immunoprecipitation experiments, confirming that the N-terminal tail is required for ColE7 interactions with TolB. The crystal structure of the N-terminal tail deleted ColE7 T-domain was determined by the multi-wavelength anomalous dispersion method at a resolution of 1.7 angstroms. The structure of the ColE7 T-domain superimposes well with the T-domain of ColE3 and TR-domain of ColB, a group A Tol-dependent colicin and a group B TonB-dependent colicin, respectively. The structural resemblance of group A and B colicins implies that the two groups of colicins may share a mechanistic connection during cellular import.
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, ROC.
authors.forename: Yi-Sheng
authors.initials: YS
authors.lastname: Cheng
authors.forename: Zhonghao
authors.initials: Z
authors.lastname: Shi
authors.forename: Lyudmila G
authors.initials: LG
authors.lastname: Doudeva
authors.forename: Wei-Zen
authors.initials: WZ
authors.lastname: Yang
authors.forename: Kin-Fu
authors.initials: KF
authors.lastname: Chak
authors.forename: Hanna S
authors.initials: HS
authors.lastname: Yuan
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D049109:Cell Proliferation; D003087:Colicins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry* / Q000166:cytology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D033903:Periplasmic Proteins / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D040681:Structural Homology, Protein
chemical_list: C508089:ColE7 protein, E coli; D003087:Colicins; D029968:Escherichia coli Proteins; D033903:Periplasmic Proteins; C062094:tolB protein, E coli