Structural highlights
Function[CEA5_ECOLX] Colicins are polypeptide toxins produced by and active against E.coli and closely related bacteria. This colicin is an endonuclease. Publication Abstract from PubMedColicin E5 cleaves tRNAs for Tyr, His, Asn and Asp in their anticodons to abolish protein synthesis in Escherichia coli. We previously showed how its C-terminal RNase domain, E5-CRD, recognizes the anticodon bases but the catalytic mechanism remained to be elucidated. Although the reaction products with 5'-OH and 2',3'-cyclic phosphate ends suggested a similar mechanism to those of RNases A and T1, E5-CRD does not have the His residues necessary as a catalyst in usual RNases. To identify residues important for the catalytic reaction, mutants as to all residues within 5 A from the central phosphorus of the scissile phosphodiester bond were prepared. Evaluation of the killing activities of the mutant colicins and the RNase activities of the mutant E5-CRDs suggested direct involvement of Arg33, Lys25, Gln29 and Lys60 in the reaction. Particularly, Arg33 plays a critical role and Ile94 provides a structural support of Arg33. Crystal structure of the complex of E5-CRD(R33Q)/dGpdUp showed structural and binding functional integrity of this mutant protein, suggesting involvement of Arg33 in the catalytic reaction. The structure of the free E5-CRD, we also determined, showed great flexibility of a flap region, which facilitates the access of Lys60 to the substrate in an induced-fit manner. Identification of the catalytic residues of sequence-specific and histidine-free ribonuclease colicin E5.,Inoue-Ito S, Yajima S, Fushinobu S, Nakamura S, Ogawa T, Hidaka M, Masaki H J Biochem. 2012 Oct;152(4):365-72. Epub 2012 Jul 18. PMID:22815490[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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