title: Association and dissociation kinetics of colicin E3 and immunity protein 3: convergence of theory and experiment.
abstract: The rapid binding of cytotoxic colicin E3 by its cognate immunity protein Im3 is essential in safeguarding the producing cell. The X-ray structure of the E3/Im3 complex shows that the Im3 molecule interfaces with both the C-terminal ribonuclease (RNase) domain and the N-terminal translocation domain of E3. The association and dissociation rates of the RNase domain and Im3 show drastically different sensitivities to ionic strength, as previously rationalized for electrostatically enhanced diffusion-limited protein-protein associations. Relative to binding to the RNase domain, binding to full-length E3 shows a comparable association rate but a significantly lower dissociation rate. This outcome is just what was anticipated by a theory for the binding of two linked domains to a protein. The E3/Im3 system thus provides a powerful paradigm for the interplay of theory and experiment.
mesh_terms: D000465:Algorithms; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D020134:Catalytic Domain; D003087:Colicins / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D012260:Ribonucleases / Q000737:chemistry / Q000378:metabolism; D055672:Static Electricity
chemical_list: D001426:Bacterial Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; C488855:ceiC protein, E coli; C007104:colicin immunity proteins; D012260:Ribonucleases