Functional variations among LOV domains as revealed by FT-IR difference spectroscopy

Area of Science:

• Biochemistry
• Spectroscopy
• Structural Biology

Background:

• LOV domains are blue-light sensing proteins crucial in various biological processes.
• Understanding the structural dynamics of LOV domains upon photoactivation is key to elucidating their signaling mechanisms.

Purpose of the Study:

• To investigate the conformational states of reactive cysteines within LOV domains from Chlamydomonas reinhardtii (LOV1 and LOV2) and Bacillus subtilis (YtvA-LOV) using light-induced FT-IR spectroscopy.
• To compare the hydrogen bonding environments and conformational homogeneity of these cysteines.
• To explore light-induced conformational changes in the STAS domain of YtvA.

Main Methods:

• Light-induced Fourier Transform Infrared (FT-IR) difference spectroscopy.
• Site-directed mutagenesis to probe cysteine roles (C32S, C83S).

Main Results:

• LOV1 cysteine C57 exhibits two distinct S-H conformations with differing hydrogen bonding strengths, potentially correlating with bi-exponential triplet state decay.
• Mutational analysis confirmed C57 as the sole source of the observed S-H stretching band in LOV1.
• LOV2 (C250) and YtvA-LOV (C62) reactive cysteines display homogenous S-H stretching bands, suggesting single conformers.
• FT-IR analysis of full-length YtvA revealed light-induced conformational alterations in the STAS domain.

Conclusions:

• The distinct S-H conformations of LOV1 C57 are critical for its photochemical behavior.
• LOV2 and YtvA-LOV reactive cysteines exist in a more uniform conformational state.
• Blue-light excitation induces structural changes beyond the LOV domain, affecting the STAS domain in YtvA.