title: The structure of TolB, an essential component of the tol-dependent translocation system, and its protein-protein interaction with the translocation domain of colicin E9.
abstract: BACKGROUND
  E colicin proteins have three functional domains, each of which is implicated in one of the stages of killing Escherichia coli cells: receptor binding, translocation and cytotoxicity. The central (R) domain is responsible for receptor-binding activity whereas the N-terminal (T) domain mediates translocation, the process by which the C-terminal cytotoxic domain is transported from the receptor to the site of its cytotoxicity. The translocation of enzymatic E colicins like colicin E9 is dependent upon TolB but the details of the process are not known.
  
  
  RESULTS
  We have demonstrated a protein-protein interaction between the T domain of colicin E9 and TolB, an essential component of the tol-dependent translocation system in E. coli, using the yeast two-hybrid system. The crystal structure of TolB, a procaryotic tryptophan-aspartate (WD) repeat protein, reveals an N-terminal alpha + beta domain based on a five-stranded mixed beta sheet and a C-terminal six-bladed beta-propeller domain.
  
  
  CONCLUSIONS
  The results suggest that the TolB-box residues of the T domain of colicin E9 interact with the beta-propeller domain of TolB. The protein-protein interactions of other beta-propeller-containing proteins, the yeast yPrp4 protein and G proteins, are mediated by the loops or outer sheets of the propeller blades. The determination of the three-dimensional structure of the T domain-TolB complex and the isolation of mutations in TolB that abolish the interaction with the T domain will reveal fine details of the protein-protein interaction of TolB and the T domain of E colicins.
authors.affiliation: Colicin Research Group, School of Biological Sciences, School of Chemical Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.
authors.forename: S
authors.initials: S
authors.lastname: Carr
authors.forename: C N
authors.initials: CN
authors.lastname: Penfold
authors.forename: V
authors.initials: V
authors.lastname: Bamford
authors.forename: R
authors.initials: R
authors.lastname: James
authors.forename: A M
authors.initials: AM
authors.lastname: Hemmings
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D003087:Colicins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D033903:Periplasmic Proteins; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D020798:Two-Hybrid System Techniques
chemical_list: D001426:Bacterial Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; D033903:Periplasmic Proteins; C007104:colicin immunity proteins; C488859:immE9 protein, E coli; C062094:tolB protein, E coli