Noncanonical Photodynamics of the Orange/Green Cyanobacteriochrome Power Sensor NpF2164g7 from the PtxD Phototaxis Regulator of Nostoc punctiforme

Journal Article · 09 April 2018 · Biochemistry

DOI: https://doi.org/10.1021/acs.biochem.7b01252 · OSTI ID:2429302

Kirpich, Julia S. ^[1]; Chang, Che-Wei ^[2]; Madsen, Dorte ^[2]; Gottlieb, Sean M. ^[2]; Martin, Shelley S. ^[2]; Rockwell, Nathan C. ^[2]; Lagarias, J. Clark  ^[2]; Larsen, Delmar S.  ^[2]

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1. University of California, Davis, CA (United States); University of California
2. University of California, Davis, CA (United States)

Forward and reverse primary (<10 ns) and secondary (>10 ns) photodynamics of cyanobacteriochrome (CBCR) NpF2164g7 were characterized by global analysis of ultrafast broadband transient absorption measurements. NpF2164g7 is the most C-terminal bilin-binding GAF domain in the Nostoc punctiforme phototaxis sensor PtxD (locus Npun_F2164). Although a member of the canonical red/green CBCR subfamily phylogenetically, NpF2164g7 exhibits an orange-absorbing ^15ZP_o dark-adapted state instead of the typical red-absorbing ^15ZP_r dark-adapted state characteristic of this subfamily. The green-absorbing ^15EP_g photoproduct of NpF2164g7 is unstable, allowing this CBCR domain to function as a power sensor. Photoexcitation of the ^15ZP_o state triggers inhomogeneous excited-state dynamics with three spectrally and temporally distinguishable pathways to generate the light-adapted ^15EP_g state in high yield (estimated at 25–30%). Although observed in other CBCR domains, the inhomogeneity in NpF2164g7 extends far into secondary relaxation dynamics (10 ns –1 ms) through to formation of ^15EP_g. In the reverse direction, the primary dynamics after photoexcitation of ^15EP_g are qualitatively similar to those of other red/green CBCRs, but secondary dynamics involve a “pre-equilibrium” step before regenerating ^15ZP_o. As a result, the anomalous photodynamics of NpF2164g7 may reflect an evolutionary adaptation of CBCR sensors that function as broadband light intensity sensors.

• Research Organization: University of California, Davis, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)
• Grant/Contract Number: SC0002395
• OSTI ID: 2429302
• Journal Information: Biochemistry, Journal Name: Biochemistry Journal Issue: 18 Vol. 57; ISSN 0006-2960
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English