Solution structure and thermodynamics of 2',5' RNA intercalation

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Understanding how small molecules bind to nucleic acids is crucial for drug development.
• The influence of the nucleic acid backbone on ligand intercalation, particularly in RNA, remains incompletely understood.
• Previous studies have primarily focused on DNA intercalation or 3',5'-linked RNA structures.

Purpose of the Study:

• To investigate the structural and thermodynamic consequences of the 2',5'-linked RNA backbone on intercalative ligand binding.
• To determine the solution structure of a proflavine-bound 2',5'-linked RNA octamer duplex.
• To compare the structural features of intercalated 2',5'-linked RNA with those of 3',5'-linked RNA and DNA.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to determine the solution structure of the proflavine-bound 2',5'-linked RNA octamer.
• X-ray crystallography data for comparison with existing 3',5'-linked RNA structures.
• Thermodynamic studies to analyze intercalator binding to both 2',5' and 3',5'-linked RNA isomers.

Main Results:

• The first NMR structure of an intercalated 2',5'-linked RNA duplex was determined.
• Differences in sugar pucker geometry and similarities in interphosphate distances were observed between 2',5' and 3',5'-linked intercalated RNA.
• The zeta backbone angle at the intercalation site prefers a trans conformation in 2',5'-linked RNA, similar to 3',5'-linked RNA, contrasting with the -gauche preference in unintercalated forms.

Conclusions:

• RNA backbone structure significantly influences intercalative binding.
• The observed conformational preferences provide insights into the flexibility required for phosphodiester-ribose backbone intercalation.
• Findings suggest a role for RNA backbone structure in the nearest-neighbor exclusion principle and highlight sensitivity of binding thermodynamics to backbone details.