ABSTRACT
Promutagenic O6-alkylguanine adducts in DNA are repaired in humans by O6-methylguanine-DNA-methyltransferase (MGMT) in an irreversible reaction. Here we describe the synthesis of a phosphoramidite that allows the preparation of oligodeoxyribonucleotides (ODNs) containing a novel tricyclic thio analogue of O6-methylguanine in which the third ring bridges the 6-thio group and C7 of a 7-deazapurine. These ODNs are very poor substrates for MGMT and poorly recognised by the alkyltransferase-like protein, Atl1. Examination of the active sites of both MGMT and Atl1 suggest large steric clashes hindering binding of the analogue. Such analogues, if mutagenic, are likely to be highly toxic.
Subject(s)
Alkyl and Aryl Transferases/chemistry , Guanine/analogs & derivatives , O(6)-Methylguanine-DNA Methyltransferase/chemistry , Oligodeoxyribonucleotides/chemistry , Sulfhydryl Compounds/chemistry , Alkyl and Aryl Transferases/metabolism , Guanine/chemistry , Guanine/metabolism , Humans , Models, Molecular , Molecular Structure , O(6)-Methylguanine-DNA Methyltransferase/metabolism , Oligodeoxyribonucleotides/chemical synthesis , Oligodeoxyribonucleotides/metabolism , Sulfhydryl Compounds/metabolismABSTRACT
We show that DNA containing a conformationally-locked anti analogue of O(6)-alkylguanine is a poor substrate for human O(6)-methylguanine-DNA methyltransferase (MGMT) and the alkyltransferase-like protein, Atl1. This highlights the requirement for the syn conformation and rationalises why certain O(6)-alkylguanines are poor MGMT substrates.
