Fluorescence Properties of a Novel Cyanobacteriochrome GAF Domain from Spirulina that Exhibits Moderate Dark Reversion

Abstract

Cyanobacteriochromes (CBCRs) are biliproteins for photoreception that are present in cyanobacteria. These proteins possess one or more unique cGMP-specific phosphodiesterase/adenylate cyclase/FhlA (GAF) domains that can covalently bind the linear tetrapyrrole (bilin). Light absorption triggers the photoisomerization of bilin between the 15Z and 15E photostates. The 15E photoproduct of some CBCR GAF domains can revert to the stable 15Z state in the absence of light. In some cases, this property makes these domains function as sensors of light intensity or as red/dark optogenetic switches. However, there have been few reports regarding the applicability of these fluorescent properties. Here, we report a red/green cyanobacteriochrome GAF domain from Spirulina subsalsa, designated SPI1085g3, which exhibited photoconversion from the red-absorbing dark state (Pr, λmax = 642 nm) to the orange-absorbing photoproduct state (Po, λmax = 590 nm), and exhibited moderate dark reversion (t1/2 = 3.3 min) from the Po state to the Pr state. The SPI1085g3 Pr state exhibited intense red fluorescence (λmax = 662 nm), with a quantum yield of 0.14. The fluorescence was switched off by red light irradiation and increased in the dark. Replacement of Cys448 of SPI1085g3 with Ser resulted in a slightly improved fluorescence quantum yield and nearly 13-fold faster dark reversion (t1/2 = 15.2 s) than that of the wild type. This novel red/dark-switchable fluorescent biliprotein expands the present repertoire and diversity of photoswitchable fluorescent protein candidates.

Phycocyanin from Arthrospira platensis as Potential Anti-Cancer Drug: Review of In Vitro and In Vivo Studies

“…Different groups reported that PC could also block G2/M cell cycle progression. This was found for pancreatic cancer cells PANC-1 [ 41 ], for human ovarian cancer cells SKOV-3 [ 79 , 80 ] and hepatoblastoma cells HepG2 [ 68 ].…”

“…PC is a blue-red fluorescent (~650 nm emission), water-soluble, non-toxic biliprotein pigment [ 33 , 41 ]. It is reported to be the main active ingredient of AP [ 42 ] and has been shown to have therapeutic properties, including anti-cancer activities [ 43 , 44 , 45 ].…”

Biliverdin incorporation into the cyanobacteriochrome SPI1085g3 from Spirulina

“…We have recently reported two novel PCB-binding CBCR GAF domains, SPI1085g2 and SPI1085g3, isolated from Spirulina subsalsa ( Wu et al, 2018 ; Jiang et al, 2021 ). PCB-binding SPI1085g2 exhibited typically reversible photoconversion between the green light-absorbing photoproduct and the red light-absorbing dark-adapted state but only with weak fluorescence ( Jiang et al, 2021 ), while PCB-binding SPI1085g3 exhibited unidirectional photoconversion and moderate dark reversion from the orange-absorbing photoproduct to the red-absorbing dark-adapted state with intense fluorescence ( Wu et al, 2018 ). The fluorescence could be switched off by illumination with red light, followed by a moderate recovery in the dark.…”

Carbon Atoms Speaking Out: How the Geometric Sensitivity of 13C Chemical Shifts Leads to Understanding the Colour Tuning of Phycocyanobilin in Cph1 and AnPixJ

“…Most intriguing, however, is the ability of CBCRs to tune their absorption over the entire range of the visible spectrum, including near-IR and near-UV [ 12 , 17 , 18 , 19 , 20 ]. The treasure of photosensors provided by nature with which organisms adapt to their environment bears high utility for biochemical applications in bioimaging and optogenetics, but also in therapy and catalysis [ 14 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ].…”

“…Phytochromes switch between red-absorbing (P ) dark states and far-red-absorbing (P ) photoproducts, [ 4 , 8 ] while the colour diversity in CBCRs is broader. Typical examples of CBCR absorption colour pairs are red/green, green/red, blue/green, red/orange, green/orange, violet/orange, blue/yellow, or blue/teal [ 12 , 14 , 18 , 19 , 20 , 34 , 42 ].…”