A universal mode of helix packing in RNA

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• RNA molecules fold into complex 3D shapes for structural and catalytic roles.
• The chemical basis for close helical packing in large RNAs remained unclear.

Purpose of the Study:

• To elucidate the chemical interactions driving helical packing in large RNA structures.
• To provide a thermodynamic explanation for conserved adenosines in RNA secondary structures.

Main Methods:

• Analysis of diverse RNA types (tRNA, catalytic RNA, in vitro-selected RNA, rRNA).
• Experimental investigation using the Tetrahymena thermophila group I ribozyme.
• Characterization of base-groove interactions and their energetic contributions.

Main Results:

• Helical packing in RNAs primarily involves single-stranded adenosines interacting with helix minor grooves.
• Adenine's shape complementarity with the minor groove enables optimal van der Waals contacts, hydrogen bonding, and hydrophobic burial.
• Similar adenosine recognition mechanisms observed in ribonucleoprotein complexes, like the signal recognition particle.

Conclusions:

• The adenine-minor groove interaction is a key, energetically favorable mechanism for RNA structural organization.
• This finding explains the conserved presence of adenosines in unpaired regions of RNA secondary structures.
• Establishes a thermodynamic basis for understanding RNA folding and function.