Localization of Fe(2+) at an RTGR sequence within a DNA duplex explains preferential cleavage by Fe(2+) and H2O2

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Iron-mediated Fenton reactions cause DNA nicking at specific sequences.
• Purine-T-G-purine (RTGR) motifs are critical regulatory elements in genes responding to iron and oxidative stress.

Purpose of the Study:

• To elucidate the molecular basis for preferential DNA nicking at RTGR sequences by iron.
• To investigate the specific binding site and interactions of Fe(2+) within the ATGA sequence using NMR.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, including one-dimensional and two-dimensional 1H NMR.
• Paramagnetic NMR line broadening studies to identify Fe(2+) interaction sites.
• Site-directed mutagenesis using 7-deazaguanine substitution and sequence alteration (ATGT) to probe binding specificity.

Main Results:

• Fe(2+) exhibits preferential, rapid, and reversible binding to the ATGA site within the RTGR duplex.
• NMR data indicate Fe(2+) interaction with the guanine N7 moiety at the ATGA site.
• Binding specificity is confirmed by experiments with modified DNA sequences and the absence of interference from Mg(2+).

Conclusions:

• The ATGA sequence within RTGR motifs serves as a specific binding site for Fe(2+), mediating preferential DNA nicking.
• Understanding this iron-DNA interaction is key to comprehending gene regulation under oxidative stress conditions.