| Summary: | 碩士 === 國立中興大學 === 生物科技學研究所 === 107 === DNA mismatches in biology are proofread by mismatch repair system. If mismatch repair system can’t proofread successfully, the outcomes may cause cancer or other genetic diseases. Echinomycin and actinomycin D are both anticancer drugs which can intercalate into DNA. Echinomycin can insert into CpG site of DNA, and actinomycin D can insert into GpC site of DNA. They can interfere the replication and transcription of DNA and then inhibit the proliferation of cancer cells. Previous studies have indicated the effects of echinomycin and actinomycin D on DNA, respectively. Therefore, we focus on the effects of echinomycin and actinomycin D on DNA structure when they are synergistically bound to DNA. We designed the sequences of d(AGCACGT), d(ACGGGCT),d(AGCCCGT), d(ACGCGCT) and d(AGCCCGT) to mix them in pairs for double stranded DNA formation. The resulted DNA duplexes contain perfect binding site of echinomycin and actinomycin D. There are one A:G mismatch, one C:G pair and one G:C pair between the binding sites of two drugs after they form DNA duplex. And then analyze the conformation of DNA-echinomycin complex and DNA-actinomycin D complex by using X-ray crystallography, respectively. We found that A:G mismatch are paired in anti-anti form and C:G pair exists as Watson-Crick base pair. There are two DNA duplexes in one assymetric unit in G:C pair complexes, where one G:C pair is like sheared Watson-Crick base pair, and the other one is paired like Hoogsteen base pair. As different types of base pairs will result in different DNA structures, these variations may have some effects on drug recognition. At last, we perform DNA melting temperature experiment to prove synergestic effect between echinomycin and actinomycin D. We hope our research can be helpful in development of anticancer drugs in combination chemotherapy in the future
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