1ayi
From Proteopedia
COLICIN E7 IMMUNITY PROTEIN IM7
Structural highlights
Function[IMM7_ECOLX] This protein is able to protect a cell, which harbors the plasmid ColE7 encoding colicin E7, against colicin E7, it binds specifically to the DNase-type colicin and inhibits its bactericidal activity. Dimeric ImmE7 may possess a RNase activity that cleaves its own mRNA at a specific site and thus autoregulates translational expression of the downstream ceiE7 gene as well as degradation of the upstream ceaE7 mRNA. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedWe 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. 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[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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