Analogue versus digital recognition of DNA by bleomycin: an effect of the carbohydrate moiety.

We have sought to determine the influence of the carbohydrate moiety of the antitumour antibiotic bleomycin on the sequence-specific cleavage of DNA. Both bleomycin A2 and deglycobleomycin A2 produce different cleavage patterns with DNA in which the 2-amino group has been removed from guanine, added to adenine, or both, as well as on a designed DNA fragment containing a few defined cleavage sites. Although each drug cleaves DNA primarily at GpT and GpC sites, the cleavage at these sites is frequently found to be stronger with deglycobleomycin compared with bleomycin A2. Conversely, in most cases the cleavage at secondary sites, in particular at ApT steps, is significantly reduced or even abolished with deglycobleomycin. The results indicate that the gulose-mannose moiety of bleomycin A2 plays a significant role in the recognition of preferred nucleotide sequences and confirm the view that both secondary structure and interaction with guanine are involved in determining sequence-specific cleavage of DNA by bleomycin.