1wpk
From Proteopedia
Methylated Form of N-terminal Transcriptional Regulator Domain of Escherichia Coli Ada Protein
Structural highlights
Function[ADA_ECOLI] Is involved in the adaptive response to alkylation damage in DNA caused by alkylating agents. Repairs O6-methylguanine and 04-methylthymine residues in alkylated DNA by a direct and irreversible transfer of the methyl group from the base to one of its own cysteine residues (Cys-321). Also specifically repairs the Sp diastereomer of DNA methylphosphotriester lesions by the same mechanism, although the methyl transfer occurs onto a different cysteine residue (Cys-38). Can not demethylate the other diastereomer, Rp-methylphosphotriester.[1] The methylation of Ada by methylphosphotriesters in DNA leads to its activation as a transcriptional regulator that activates the transcription of its own gene, ada, and other alkylation resistance genes, alkA, alkB and aidB.[2] 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 PubMedThe N-terminal 16-kDa domain of Escherichia coli Ada protein (N-Ada16k) repairs DNA methyl phosphotriester lesions by an irreversible methyl transfer to its cysteine residue. Upon the methylation, the sequence-specific DNA binding affinity for the promoter region of the alkylation resistance genes is enhanced by 10(3)-fold. Then, it acts as a transcriptional regulator for the methylation damage. In this paper, we identified the methyl acceptor residue of N-Ada16k and determined the solution structure of the methylated form of N-Ada16k by using NMR and mass spectrometry. The results of a 13C-filtered 1H-13C HMBC experiment and MALDI-TOF MS and MS/MS experiments clearly showed that the methyl acceptor residue is Cys38. The solution structure revealed that it has two distinct subdomains connected by a flexible linker loop: the methyltransferase (MTase) subdomain with the zinc-thiolate center, and the helical subdomain with a helix-turn-helix motif. Interestingly, there is no potential hydrogen bond donor around Cys38, whereas the other three cysteine residues coordinated to a zinc ion have potential donors. Hence, Cys38 could retain its inherent nucleophilicity and react with a methyl phosphotriester. Furthermore, the structure comparison shows that there is no indication of a remarkable conformational change occurring upon the methylation. This implies that the electrostatic repulsion between the negatively charged DNA and the zinc-thiolate center may avoid the contact between the MTase subdomain and the DNA in the nonmethylated form. Thus, after the Cys38 methylation, the MTase subdomain can bind the cognate DNA because the negative charge of the zinc-thiolate center is reduced. The solution structure of the methylated form of the N-terminal 16-kDa domain of Escherichia coli Ada protein.,Takinowaki H, Matsuda Y, Yoshida T, Kobayashi Y, Ohkubo T Protein Sci. 2006 Mar;15(3):487-97. Epub 2006 Feb 1. PMID:16452614[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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