Temperature dependence of anisotropic protein backbone dynamics

Area of Science:

• Biophysics
• Structural Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Nuclear Magnetic Resonance (NMR) spin relaxation, particularly (15)N NMR, is a standard technique for studying protein backbone dynamics.
• The (15)N-(1)H vector's reorientational dynamics are commonly used to infer overall protein backbone motion.

Purpose of the Study:

• To investigate if (15)N-(1)H vector motions accurately represent the overall protein backbone dynamics.
• To analyze the temperature dependence of (15)N-(1)H and (13)CO-(13)C(alpha) reorientational dynamics in small proteins.

Main Methods:

• Utilized NMR cross-correlated relaxation experiments to measure (13)CO-(13)C(alpha) reorientational dynamics.
• Analyzed the temperature dependence of (15)N-(1)H and (13)CO-(13)C(alpha) order parameters in binase and ubiquitin.

Main Results:

• A minimal decrease (2.5%) in (15)N-(1)H order parameters was observed between 5 and 30°C.
• A substantial decrease (10%) in (13)CO-(13)C(alpha) order parameters occurred over the same temperature range.
• Identified significant polypeptide-backbone motions at room temperature not detected by (15)N-(1)H vector dynamics, contradicting the crank-shaft model.

Conclusions:

• Standard (15)N NMR relaxation measurements may underestimate protein backbone dynamics and associated entropy.
• Relying solely on (15)N-(1)H vector dynamics provides an incomplete picture of protein flexibility.
• Further investigation using complementary NMR techniques is crucial for a comprehensive understanding of protein dynamics.