O6-alkylguanine-DNA alkyltransferase: low pKa and high reactivity of cysteine 145.

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Guengerich FP, Fang Q, Liu L, Hachey DL, Pegg AE

O6-alkylguanine-DNA alkyltransferase: low pKa and high reactivity of cysteine 145.

Biochemistry. 2003 Sep 23;42(37):10965-70.

PubMed ID

12974631 [ View in PubMed

]

Abstract

The active site cysteine of human O(6)-alkylguanine-DNA alkyltransferase (hAGT), Cys145, was shown to be highly reactive with model electrophiles unrelated to substrates, including 1-chloro-2,4-dinitrobenzene. The high reactivity suggested that the Cys145 thiolate anion might be stable at neutral pH. The pK(a) was estimated from plots of UV spectra (A(239)) and reactivity toward 4,4'-dithiopyridine vs pH. The estimated pK(a) for hAGT was 4-5, depending upon the method used, and near that of the extensively characterized papain Cys25. Rates of reaction with 4,4'-dithiopyridine were similar for the thiolate forms of hAGT, papain, glutathione, and the bacterial hAGT homologue Ogt (the pK(a) of the latter was 5.4). Bound Zn(2+) has previously been shown to be required for the catalytic activity of hAGT (Rasimas, J. J. et al. (2003) Biochemistry 42, 980-990). Zn(2+) was shown to be required for the low pK(a) of hAGT. The high reactivity of hAGT Cys145 is postulated to be important in normal catalytic function, in cross-linking reactions involving bis-electrophiles, and in inhibition of the DNA repair function of hAGT by electrophiles.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Dinitrochlorobenzene	Methylated-DNA--protein-cysteine methyltransferase	Protein	Humans	Unknown	Not Available	Details