Size, shape, and flexibility of RNA structures.

Area of Science:

• Structural Biology
• Biophysics
• Computational Biology

Background:

• Understanding RNA structure and interactions is crucial for molecular biology.
• RNA molecules fold into complex 3D structures essential for their function.
• Analyzing RNA packing and flexibility provides insights into biological mechanisms.

Purpose of the Study:

• To determine the size and flexibility of folded RNA structures using structural data.
• To characterize the shape and packing of RNA molecules and ribosome subunits.
• To investigate the relationship between RNA size, shape, flexibility, and folding.

Main Methods:

• Utilized RNA structure coordinates from the Protein Data Bank.
• Applied Flory scaling laws to analyze RNA size (radius of gyration).
• Computed shape parameters (asphericity, shape parameter S) using moment of inertia tensor eigenvalues.
• Extracted persistence length (flexibility) by fitting distance distribution to the wormlike chain model.

Main Results:

• RNA size follows Flory scaling: R(G) ≈ 5.5N^(1/3) Å.
• Many folded RNA structures are aspherical, with a prolate shape (S>0).
• RNA flexibility (persistence length) scales with size: l(p) ≈ 1.5N^(0.33) Å.
• Ribosome subunits (70S, 50S) are more spherical than most RNA molecules.
• 50S subunit's globularity results from numerous small helices linked by bulges and loops.

Conclusions:

• RNA size, shape, and flexibility are predictable based on nucleotide count and folding principles.
• The observed scaling relationships suggest a correlation between secondary and tertiary structure stabilization energies.
• Ribosome assembly may involve pre-folding of individual RNA components.