Crystal structure of actinomycin D bound to the CTG triplet
repeat sequences linked to neurological diseases.
Nucleic
Acids Res 2002 Nov 15;30(22):4910-7
Hou MH, Robinson H, Gao YG, Wang AH.
Institute of Biological Chemistry, Academia Sinica, Taipei, 115 Taiwan.
The potent anticancer drug actinomycin D (ActD) acts by binding to DNA GpC
sequences, thereby interfering with essential biological processes including
replication, transcription and topoisomerase. Certain neurological diseases
are correlated with expansion of (CTG)n trinucleotide sequences, which contain
many contiguous GpC sites separated by a single base pair. In order to
characterize the binding of ActD to CTG triplet repeat sequences, we carried
out heat denaturation and CD analyses, which showed that adjacent GpC
sequences flanking a T:T mismatch are preferred ActD-binding sites, and that
ActD binding results in a conformational transition to A-type structure. The
structural basis of the strong binding of ActD to neighboring GpC sites
flanking a T:T mismatch was provided by the crystal structure of ActD bound to
ATGCTGCAT, which contains a CTG triplet sequence. Binding of two ActD
molecules to GCTGC causes a kink in the DNA helix. In addition, using a
synthetic self-priming DNA model, 5'-(CAG)4(CTG)(16)-3', we observed that ActD
can trap the cruciform or duplexes of (CTG)n and interfere with the expansion
process of CTG triplet repeats as shown by gel electrophoretic expansion
assay. Our results may provide the possible biological consequence of ActD
bound to CTG triplet repeat sequences.
