1imp
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COLICIN E9 IMMUNITY PROTEIN IM9, NMR, 21 STRUCTURES
OverviewOverview
The 86-amino acid colicin E9 immunity protein (Im9), which inhibits the, DNase activity of colicin E9, has been overexpressed in Escherichia coli, and isotopically enriched with 15N and 13C. Using the 3D CBCANH and, CBCA(CO)NH experiments, we have almost completely assigned the backbone, 13C resonances and extended previously reported 15N/1H backbone, assignments [Osborne et al. (1994), Biochemistry 33, 12347-12355]. Side, chain assignments for almost all residues were made using the 3D 13C, HCCH-TOCSY experiment allied to previous 1H assignments. Sixty solution, structures of Im9 were determined using the DIANA program on the basis of, 1210 distance restraints and 56 dihedral angle restraints. The 30, lowest-energy structures were then subjected to a slow-cooling simulated, annealing protocol using XPLOR and the 21 lowest-energy structures, satisfying the geometric restraints chosen for further analysis. The Im9, structure is well-defined except for the termini and two solvent-exposed, loops between residues 28-32 and 57-64. The average RMSD about the average, structure of residues 4-84 was 0.94 A for all heavy atoms and 0.53 A for, backbone C alpha, C = O, and N atoms. The Im9 fold is novel and can be, considered a distorted antiparallel four-helix bundle, in which the third, helix is rather short, being terminated close to its N-terminal end by a, proline at its C-terminus. The structure fits in well with available, kinetic and biochemical data concerning the interaction between Im9 and, its target DNase. Important residues of Im9 that govern specificity are, located on the molecular surface in a region rich in negatively charged, groups, consistent with the proposed electrostatically steered association, [Wallis et al. (1995a), Biochemistry 34, 13743-13750].
About this StructureAbout this Structure
1IMP is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
ReferenceReference
Three-dimensional solution structure and 13C nuclear magnetic resonance assignments of the colicin E9 immunity protein Im9., Osborne MJ, Breeze AL, Lian LY, Reilly A, James R, Kleanthous C, Moore GR, Biochemistry. 1996 Jul 23;35(29):9505-12. PMID:8755730
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