An NMR Confirmation for Increased Folded State Entropy Following Loop Truncation

Area of Science:

• Protein dynamics and stability
• Biophysical chemistry
• Structural biology

Background:

• Flexible loop regions in proteins are crucial for function and stability.
• Previous research suggested loop ordering entropy dominates folding energetics.
• Prior studies on human acylphosphatase (hmAcP) indicated folded state entropy is key for stability upon loop truncation.

Purpose of the Study:

• To investigate the effect of loop truncation on hmAcP backbone dynamics.
• To confirm the contribution of folded state entropy to protein stability using NMR spectroscopy.
• To quantitatively measure the impact of loop truncation on protein conformational flexibility.

Main Methods:

• Utilized 15N NMR spectroscopy to study hmAcP backbone dynamics on the picosecond-nanosecond timescale.
• Employed NMR-relaxation-derived N-H squared generalized order parameters.
• Compared NMR findings with existing all-atom molecular dynamics simulations.

Main Results:

• Loop truncation significantly increased protein conformational flexibility.
• NMR data showed enhanced conformational entropy in the folded state of hmAcP.
• Results from NMR spectroscopy generally agreed with molecular dynamics simulations.

Conclusions:

• Loop truncation in hmAcP enhances folded state entropy, contributing to thermodynamic stabilization.
• NMR spectroscopy provides direct, quantitative evidence for increased conformational flexibility and entropy.
• The findings support the significant role of folded state entropy in protein stability modulation.