2gyk

[[Image:2gyk.jpg|left|200px]]

'''Crystal structure of the complex of the Colicin E9 DNase domain with a mutant immunity protein, IMME9 (D51A)'''

==Overview==

The crystal structure of the cytotoxic endonuclease domain from the bacterial toxin colicin E9 in complex with its cognate immunity protein Im9 reveals that the inhibitor does not bind at the active site, the core of which comprises the HNH motif found in intron-encoded homing endonucleases, but rather at an adjacent position leaving the active site exposed yet unable to bind DNA because of steric and electrostatic clashes with incoming substrate. Although its mode of action is unorthodox, Im9 is a remarkably effective inhibitor since it folds within milliseconds and then associates with its target endonuclease at the rate of diffusion to form an inactive complex with sub-femtomolar binding affinity. This hyperefficient mechanism of inhibition could be well suited to other toxic enzyme systems, particularly where the substrate is a polymer extending beyond the boundaries of the active site.

2GYK is a [[Protein complex]] structure of sequences from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2GYK OCA].

Structural and mechanistic basis of immunity toward endonuclease colicins., Kleanthous C, Kuhlmann UC, Pommer AJ, Ferguson N, Radford SE, Moore GR, James R, Hemmings AM, Nat Struct Biol. 1999 Mar;6(3):243-52. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/10074943 10074943]

[[Category: Protein complex]]

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