Global conformational changes upon receptor stimulation in photoactive yellow protein

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Biological signal transduction is initiated by receptor protein activation.
• Understanding stimulus-induced activation mechanisms and protein conformational changes is crucial for signaling research.

Purpose of the Study:

• To investigate the large structural changes in photoactive yellow protein (PYP) upon light activation.
• To elucidate the mechanism of PYP photoactivation and its implications for general receptor activation.

Main Methods:

• Fourier transform infrared (FTIR) difference spectroscopy to detect backbone structural changes.
• Light-induced hydrogen/deuterium (H/D) exchange monitored by electrospray ionization mass spectrometry and FTIR spectroscopy.
• Thermodynamic studies to analyze heat capacity changes during activation and decay.

Main Results:

• Light absorption by the p-coumaric acid (pCA) chromophore induces a putative signaling state (pB) from the initial state (pG).
• Extensive protein backbone rearrangements, affecting both solvent-accessible and core regions, were observed.
• 23% of buried amide groups in pG become solvent-exposed in pB, indicating significant structural alterations.
• Thermodynamic analysis revealed a negative heat capacity change (-2.35 kJ/(mol/K)) during pB activation, independent of pH.

Conclusions:

• Photoactive yellow protein (PYP) undergoes substantial conformational changes upon light activation.
• The observed structural dynamics provide a framework for understanding general receptor activation mechanisms.
• This study offers deep insights into the molecular basis of biological signal transduction.