Abstract
Interaction of the TolB box of Group A colicins with the TolB protein in the periplasm of Escherichia coli cells promotes transport of the cytotoxic domain of the colicin across the cell envelope. The crystal structure of a complex between a 107-residue peptide (TA1–107) of the translocation domain of colicin A (ColA) and TolB identified the TolB box as a 12-residue peptide that folded into a distorted hairpin within a central canyon of the β-propeller domain of TolB. Comparison of this structure with that of the colicin E9 (ColE9) TolB box–TolB complex, together with site-directed mutagenesis of the ColA TolB box residues, revealed important differences in the interaction of the two TolB boxes with an overlapping binding site on TolB. Substitution of the TolB box residues of ColA with those of ColE9 conferred the ability to competitively recruit TolB from Pal but reduced the biological activity of the mutant ColA. This datum explains (i) the difference in binding affinities of ColA and ColE9 with TolB, and (ii) the inability of ColA, unlike ColE9, to competitively recruit TolB from Pal, allowing an understanding of how these two colicins interact in a different way with a common translocation portal in E. coli cells.
Highlights
Many proteins of eubacterial or of eucaryotic origin contain stretches of > 30 amino acids that are natively disordered regions (NDRs) (Ward et al, 2004)
Previous mutagenesis studies have shown that the G38 residue of colicin E9 (ColE9) is not essential for activity (Garinot-Schneider et al, 1997), and that the S37 residue of ColE9 can be substituted by threonine without significant loss of function (Hands et al, 2005)
We assume that substitution of G14 of colicin A (ColA) to N14 or S14 of Col28b and Klebicin D respectively, and G36 of ColE9 to N34 of Alveicin A would not affect biological activity
Summary
Many proteins of eubacterial or of eucaryotic origin contain stretches of > 30 amino acids that are natively (intrinsically) disordered regions (NDRs) (Ward et al, 2004). Native disorder occurs in regions with a high glycine content and a prevalence of charged or polar residues that preclude the formation of a hydrophobic core or stable three-dimensional fold. Such NDRs are important in many biological processes such as transcription, translation, intracellular signalling and host– pathogen interactions where their roles are to bind to other macromolecules to form complexes (Dyson and Wright, 2005). NDRs undergo disorder-order transitions on binding a partner molecule (Wright and Dyson, 1999). Recent studies with colicins have highlighted the important role of NDRs in the complex protein–protein interactions that drive cellular uptake of these proteins (Collins et al, 2002; Macdonald et al, 2004; Tozawa et al, 2005)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
