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Free keywords:
BLUF domain; Blue-light-regulated phosphodiesterase (BlrP1); Klebsiella pneumoniae; Blue-light receptor; FAD; Absorption spectroscopy; Fluorescence spectroscopy; Photo-cycle; Photo-induced electron transfer; Photo-reduction
Abstract:
The BlrP1 protein from the enteric bacterium Klebsiella pneumoniae consists of a BLUF and an EAL domain and may activate c-di-GMP phosphodiesterase by blue-light. The full-length protein, BlrP1, and its BLUF domain, BlrP1_BLUF, are characterized by optical absorption and emission spectroscopy. The cofactor FAD in its oxidized redox state (FADox) is brought from the dark-adapted receptor state to the 10-nm red-shifted putative signalling state by violet light exposure. The recovery to the receptor state occurs with a time constant of about 1 min. The quantum yield of signalling state formation is about 0.17 for BlrP1_BLUF and about 0.08 for BlrP1. The fluorescence efficiency of the FADox cofactor is small due to photo-induced reductive electron transfer. Prolonged light exposure converts FADox in the signalling state to the fully reduced hydroquinone form FADredH− and causes low-efficient chromophore release with subsequent photo-degradation. The photo-cycle and photo-reduction dynamics in the receptor state and in the signalling state are discussed.
