1ayi
From Proteopedia
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'''COLICIN E7 IMMUNITY PROTEIN IM7''' | '''COLICIN E7 IMMUNITY PROTEIN IM7''' | ||
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[[Category: Pauptit, R A.]] | [[Category: Pauptit, R A.]] | ||
[[Category: Wallis, R.]] | [[Category: Wallis, R.]] | ||
| - | [[Category: | + | [[Category: Bacteriocin]] |
| - | [[Category: | + | [[Category: Dnase inhibitor]] |
| - | [[Category: | + | [[Category: E colicin]] |
| - | [[Category: | + | [[Category: Protein-protein interaction]] |
| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 10:50:46 2008'' | |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | + | |
Revision as of 07:50, 2 May 2008
COLICIN E7 IMMUNITY PROTEIN IM7
Overview
We report the first detailed comparison of two immunity proteins which, in conjunction with recent protein engineering data, begins to explain how these structurally similar proteins are able to bind and inhibit the endonuclease domain of colicin E9 (E9 DNase) with affinities that differ by 12 orders of magnitude. In the present work, we have determined the X-ray structure of the Escherichia coli colicin E7 immunity protein Im7 to 2.0 A resolution by molecular replacement, using as a trial model the recently determined NMR solution structure of Im9. Whereas the two proteins adopt similar four-helix structures, subtle structural differences, in particular involving a conserved tyrosine residue critical for E9 DNase binding, and the identity of key residues in the specificity helix, lie at the heart of their markedly different ability to bind the E9 DNase. Two other crystal structures were reported recently for Im7; in one, Im7 was a monomer and was very similar to the structure reported here, whereas in the other it was a dimer to which functional significance was assigned. Since this previous work suggested that Im7 could exist either as a monomer or a dimer, we used analytical ultracentrifugation to investigate this question further. Under a variety of solution conditions, we found that Im7 only ever exists in solution as a monomer, even up to protein concentrations of 15 mg/ml, casting doubt on the functional significance of the crystallographically observed dimer. This work provides a structural framework with which we can understand immunity-protein specificity, and in addition we believe it to be the first successfully refined crystal structure solved by molecular replacement using an NMR trial model with less than 100% sequence identity.
About this Structure
1AYI is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
A structural comparison of the colicin immunity proteins Im7 and Im9 gives new insights into the molecular determinants of immunity-protein specificity., Dennis CA, Videler H, Pauptit RA, Wallis R, James R, Moore GR, Kleanthous C, Biochem J. 1998 Jul 1;333 ( Pt 1):183-91. PMID:9639578 Page seeded by OCA on Fri May 2 10:50:46 2008
