Actinomycin D binding to unstructured, single-stranded DNA.

Area of Science:

• Molecular Biology
• Biochemistry
• Pharmacology

Background:

• Actinomycin D is an anticancer drug known for binding double-stranded DNA and inhibiting transcription.
• Its binding to single-stranded DNA is implicated in biological activities, such as inhibiting HIV reverse transcriptase.
• Specific single-stranded DNA sequences, like d(GTTAACCATAG), exhibit high affinity for actinomycin D.

Purpose of the Study:

• To investigate the sequence and length requirements for actinomycin D binding to single-stranded DNA.
• To identify the minimal sequence length necessary for high-affinity binding.
• To explore the role of DNA secondary structure in actinomycin D binding.

Main Methods:

• Utilized a fluorescent analog, 7-aminoactinomycin D, to monitor drug binding.
• Studied the binding affinity to d(GTTAACCATAG) and 31 related single-stranded DNA oligomers.
• Determined binding affinities (Kd values) for various oligonucleotide sequences and lengths.

Main Results:

• High-affinity binding required a TAG sequence at or near the 3'-terminus.
• An eight-nucleotide sequence, d(AACCATAG), demonstrated the highest drug affinity (Kd = 125 nM).
• This minimal binding sequence is unstructured in the absence of actinomycin.

Conclusions:

• High-affinity binding of actinomycin D to single-stranded DNA does not necessitate pre-existing secondary structure.
• An induced-fit mechanism is proposed for actinomycin D binding to specific single-stranded DNA sequences.
• The minimum length for tight binding involves at least eight nucleotides.