Probing anisotropic structure changes in proteins with picosecond time-resolved small-angle X-ray scattering

Area of Science:

• Biophysics
• Structural Biology
• Protein Dynamics

Background:

• Photoactive yellow protein (PYP) is a model system for studying light-induced protein conformational changes.
• Understanding protein dynamics is crucial for elucidating biological functions.

Purpose of the Study:

• To investigate protein size and shape changes in solution after photoactivation of PYP.
• To achieve high time resolution (∼150 ps) for observing early structural dynamics.

Main Methods:

• Utilized time-resolved small-angle X-ray scattering (SAXS) combined with photoselection.
• Overcame orientational averaging inherent in solution scattering methods.

Main Results:

• Photoactivation of the p-coumaric acid (pCA) chromophore induced prompt protein compaction (∼0.3%) along the transition dipole moment.
• Observed orthogonal expansion and a net volume decrease (∼-0.25%).
• Significant strain relief occurred during the pR0 to pR1 transition (1.8 ns).

Conclusions:

• Early structural dynamics in PYP crystals are mirrored in solution.
• The observed strain may drive the formation of the signaling state (pB).
• Time-resolved SAXS provides detailed structural insights into photoactivated proteins.