Demonstration of an Alternative Mechanism for G-to-G Cross-Link Formation


The cross-link dG-to-dG is an important product of DNA nitrosation. Its formation has commonly been attributed to nucleophilic substitution of N2 in a guaninediazonium ion by guanine, while recent studies suggest guanine addition to a cyanoamine derivative formed after dediazoniation, deprotonation, and pyrimidine ring-opening. The chemical viability of the latter mechanism is supported here by the experimental demonstration of rG-to-aG formation via rG addition to a synthetic cyanoamine derivative. Thus, all known products of nitrosative guanine deamination are consistent with the postulate of pyrimidine ring-opening. This postulated mechanism not only explains what is already known but also suggests that other products and other cross-links also might be formed in DNA deamination. The study suggests one possible new product: the structure isomer aG(N1)-to-rG(C2) of the classical G(N2)-to-G(C2) cross-link. While the formation of aG(N2)-to-rG(C2) has been established by chemical synthesis, the structure isomer aG(N1)-to-rG(C2) has been assigned tentatively based on its MS/MS spectrum and because this assignment is reasonable from a mechanistic perspective. Density functional calculations show preferences for the amide-iminol tautomer of the classical cross-link G(N2)-to-G(C2) and the amide-amide tautomer of G(N1)-to-G(C2). Moreover, the results suggest that both cross-links are of comparable thermodynamic stability, and that there are no a priori energetic or structural reasons that would prevent the formation of the structure isomer in the model reaction or in DNA.



Keywords and Phrases

Crosslinking; Isomers; Nitrogen Compounds; Structure (Composition); Substitution Reactions; Synthesis (Chemical); Thermodynamic Stability; Deamination; Deprotonation; DNA Nitrosation; Pyrimidine Ring-Opening; DNA; Amide; Diazonium Compound; Guanidine Derivative; Guanine; Nitrile; Pyrimidine; Cross Linking; Density Functional Theory; Isomer; Mass Spectrometry; Nitrosation; Reaction Analysis; Ring Opening; Synthesis; Thermodynamics; Thermostability; Amines; Aminoimidazole Carboxamide; Guanosine; Models; Molecular; Oligonucleotides; Ribonucleosides

International Standard Serial Number (ISSN)

0002-7863; 1520-5126

Document Type

Article - Journal

Document Version


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© 2005 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 2005

PubMed ID