Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The major human apurinic/apyrimidinic (AP) endonuclease (class II) is known to cleave DNA 5' adjacent to an AP site, which is probably the most common DNA damage produced hydrolytically or by glycosylase-mediated removal of modified bases. p-Benzoquinone (pBQ), one of the major benzene metabolites, reacts with DNA to form bulky exocyclic adducts. Herein we report that the human AP endonuclease directly catalyzes incision in a defined oligonucleotide containing 3,N4-benzetheno-2'-deoxycytidine (pBQ-dC) without prior generation of an AP site. The enzyme incises the oligonucleotide 5' to the adduct and generates 3'-hydroxyl and 5'-phosphoryl termini but leaves the pBQ-dC on the 5' terminus of the cleavage fragment. The AP function of the enzyme is not involved in this action, as no preexisting AP site is present nor is a DNA glycosylase activity involved. Nicking of the pBQ-dC adduct also leads to the same "dangling base" cleavage when two Escherichia coli enzymes, exonuclease III and endonuclease IV, are used. Our finding of this unusual mode of action used by both human and bacterial AP endonucleases raises important questions regarding the requirements for substrate recognition and catalytic active site(s) for this essential cellular repair enzyme. We believe this to be the first instance of the presence of a bulky carcinogen adduct leading to this unusual mode of action.
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PMID:An unusual mechanism for the major human apurinic/apyrimidinic (AP) endonuclease involving 5' cleavage of DNA containing a benzene-derived exocyclic adduct in the absence of an AP site. 894 4

p-Benzoquinone (p-BQ), a stable metabolite of the human carcinogen benzene, forms two-ring benzetheno exocyclic base adducts with C, A, and G bases in DNA. As a part of a project for studying the biological effect of the p-BQ adducts, we report here on the first biophysical characterization of oligodeoxyribonucleotide duplexes containing a single site-specific p-BQ-C, using thermal denaturation and circular dichroism (CD). We find that the thermal and thermodynamic stabilities of the control duplex are reduced by p-BQ-C. The Tm value decreases by 12.6 degrees C at the duplex concentration of 1.5 microM and the Delta G o by 10.2 kcal/mol. The latter was determined from the concentration dependence of the Tm values. The destabilization has little dependence on the nature of the opposite base. This reduction is higher than that of the single base mismatches studied (-4.9 to -7.9 kcal/mol) and is close to that observed with an adjacent double mismatch-containing duplex (-11.3 kcal/mol). The overall B-conformation of the duplex with a p-BQ-C is, however, only slightly altered, relative to the parent duplex, as shown by CD spectra. The p-BQ-C-containing duplex has been found recently to be a good substrate for the major human AP endonuclease as compared to an abasic site-containing duplex [Hang, B., et al. (1997) Biochemistry 36, 15411-15418]. We now find that the thermodynamic properties and the localized conformational changes of a p-BQ-C-containing duplex are apparently related to those reported for a duplex containing an abasic site.
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PMID:A single cyclic p-benzoquinone adduct can destabilize a DNA oligonucleotide duplex. 954 3