Photochemical reactions of the LOV and the LOV-linker domains of the blue light sensor protein YtvA
Seokwoo Choi, Yusuke Nakasone, Klaas J. Hellingwerf, Masahide Terazima
YtvA is a blue light sensor protein composed of an N-terminal LOV (Light–Oxygen–Voltage) domain, a linker helix, and the C-terminal Sulfate Transporter and Anti Sigma factor antagonists domain. YtvA is believed to act as a positive regulator for light and salt stress responses by regulating the σB transcription factor. Although its biological function has been studied, the reaction dynamics and the molecular mechanism underlying the functioning has not been understood well. To better understand the signaling mechanism, we studied the reaction of the LOV domain (YLOV; [aa] 26–127), the LOV domain with its N-terminal extension (N-YLOV; 1–127), the LOV domain with its C-terminal linker helix (YLOV-linker; 26–147), and the YLOV domain with the N-terminal extension and the C-terminal linker helix (N-YLOV-linker; 1–147) using the transient grating method. The signals of all constructs showed adduct formation, thermal diffusion, and molecular diffusion. YLOV showed no change in the diffusion coefficient (D), while the other three constructs showed a significant decrease in D within ~70 μs after photoexcitation. This indicates that conformational changes in both the N- and C-terminal helices of the YLOV domain indeed do occur. The time constant in the YtvA derivatives was much faster than the corresponding dynamics of phototropins. Interestingly, an additional reaction was observed as a volume expansion as well as a slight increase in D only when both helices were included. These findings suggest that although the rearrangement of the N- and C-terminal helices occurs independently at the fast time scale, this change induces an additional conformational change only when both helices are present.
Circular dichroism, Secondary structure, Biochemistry