Solution structure and dynamics of ribonuclease Sa.

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Ribonuclease Sa (RNase Sa) is a key enzyme in biological processes.
• Understanding protein structure and dynamics in solution is crucial for elucidating function.
• Previous studies primarily relied on crystal structures, potentially limiting insights into solution behavior.

Purpose of the Study:

• To characterize the solution structure and dynamics of ribonuclease Sa (RNase Sa).
• To compare solution structures with existing crystal structures.
• To investigate the flexibility and conformational entropy of RNase Sa folding.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed.
• Distance constraints from Nuclear Overhauser Effect (NOE) and disulfide bonds were utilized.
• (15)N relaxation experiments (R1, R2, and NOE) were performed at 600 MHz.

Main Results:

• High-resolution solution structures of RNase Sa were obtained, showing similarity to crystal structures, particularly in secondary structure.
• Distinct conformations were observed in the Pro45-Ser48 loop, and reduced flipping rates for tyrosines 51, 52, and 55.
• Five flexible segments were identified through (15)N relaxation analysis, indicating dynamic regions within the protein.
• Amide protons with reduced exchange rates were located in various secondary structure elements, including interior beta-strands, alpha-helix, 3/10 helix, and disulfide-linked beta-strand.

Conclusions:

• RNase Sa exhibits greater flexibility in solution compared to its crystalline state.
• The conformational entropy change during RNase Sa folding is likely smaller than previously estimated.
• NMR provides valuable insights into protein dynamics and conformational states in solution.