Slow Conformational Changes of Blue Light Sensor BLUF Proteins in Milliseconds

Area of Science:

• Biochemistry
• Photobiology
• Protein Dynamics

Background:

• Blue light sensor using flavin (BLUF) proteins mediate light signal transduction.
• BLUF proteins undergo spectral changes upon blue light excitation, traditionally thought to occur within nanoseconds.

Purpose of the Study:

• To investigate the temporal dynamics of spectral changes in BLUF proteins.
• To elucidate the role of protein domains and specific residues in BLUF photoreception.

Main Methods:

• Spectroscopic analysis of wild-type and mutant BLUF proteins (AppA, OaPAC, BlrP1, YcgF, PapB, SyPixD, TePixD).
• Time-resolved kinetic measurements in the millisecond timescale.
• Site-specific mutagenesis and domain deletion studies.

Main Results:

• Discovery of slow millisecond (τ1- and τ2-phase) reaction kinetics in BLUF proteins, contrary to prior nanosecond assumptions.
• The slower τ2-phase dynamics are influenced by the C-terminal region adjacent to the BLUF domain.
• The τ1-phase is consistently observed across all BLUF proteins and is linked to the role of tryptophan residues within the BLUF domain.

Conclusions:

• The millisecond dynamics are critical indicators of conformational changes in the C-terminal region, essential for BLUF protein function.
• Tryptophan residues within the BLUF domain play a significant role in the observed slow dynamics.
• A novel reaction scheme for BLUF protein activation is proposed based on these findings.