Biomedical subjects

Sarah C Trewick

Publications and source records attributed to Sarah C Trewick.

3 recordsLinked to original sources

PubMed2005

Methylation: lost in hydroxylation?

Methylation of histone tails is a key determinant in forming active and silent states of chromatin. Histone methylation was regarded as irreversible until the recent identification of a lysine-specific histone demethylase (LSD1), which acts specifically on mono- and dimethylated histone H3 lysine 4. Here, we propose that the fission yeast protein Epe1 is a putative histone demethylase that could act by oxidative demethylation. Epe1 modulates the stability of silent chromatin and contains a JmjC domain. The Epe1 protein can be modelled onto the structure of the 2-oxoglutarate-Fe(II)-dependent dioxygenase, factor inhibiting hypoxia inducible factor (FIH), which is a protein hydroxylase that also contains a JmjC domain. Thus, Epe1 and certain other chromatin-associated JmjC-domain proteins may be protein hydroxylases that catalyse a novel histone modification. Another intriguing possibility is that, by hydroxylating the methyl groups, Epe1 and certain other JmjC-domain proteins may be able to demethylate mono-, di- or trimethylated histones.

Amino Acid Sequence↗

PubMed2002

Reversal of DNA alkylation damage by two human dioxygenases.

The Escherichia coli AlkB protein protects against the cytotoxicity of methylating agents by repair of the DNA lesions 1-methyladenine and 3-methylcytosine, which are generated in single-stranded stretches of DNA. AlkB is an alpha-ketoglutarate- and Fe(II)-dependent dioxygenase that oxidizes the relevant methyl groups and releases them as formaldehyde. Here, we identify two human AlkB homologs, ABH2 and ABH3, by sequence and fold similarity, functional assays, and complementation of the E. coli alkB mutant phenotype. The levels of their mRNAs do not appear to correlate with cell proliferation but tissue distributions are different. Both enzymes remove 1-methyladenine and 3-methylcytosine from methylated polynucleotides in an alpha-ketoglutarate-dependent reaction, and act by direct damage reversal with the regeneration of the unsubstituted bases. AlkB, ABH2, and ABH3 can also repair 1-ethyladenine residues in DNA with the release of acetaldehyde.

Adenine↗

PubMed2002

Oxidative demethylation by Escherichia coli AlkB directly reverts DNA base damage.

Methylating agents generate cytotoxic and mutagenic DNA damage. Cells use 3-methyladenine-DNA glycosylases to excise some methylated bases from DNA, and suicidal O(6)-methylguanine-DNA methyltransferases to transfer alkyl groups from other lesions onto a cysteine residue. Here we report that the highly conserved AlkB protein repairs DNA alkylation damage by means of an unprecedented mechanism. AlkB has no detectable nuclease, DNA glycosylase or methyltransferase activity; however, Escherichia coli alkB mutants are defective in processing methylation damage generated in single-stranded DNA. Theoretical protein fold recognition had suggested that AlkB resembles the Fe(ii)- and alpha-ketoglutarate-dependent dioxygenases, which use iron-oxo intermediates to oxidize chemically inert compounds. We show here that purified AlkB repairs the cytotoxic lesions 1-methyladenine and 3-methylcytosine in single- and double-stranded DNA in a reaction that is dependent on oxygen, alpha-ketoglutarate and Fe(ii). The AlkB enzyme couples oxidative decarboxylation of alpha-ketoglutarate to the hydroxylation of these methylated bases in DNA, resulting in direct reversion to the unmodified base and the release of formaldehyde.

Adenine↗