To activate a G protein-coupled receptor permanently with cell surface photodynamic action in the gastrointestinal tract

Table 1 Comparison of the properties of novel types of G protein coupled receptors

Abbreviation	RASSL/DREADD	GPCR-ABSO
Activation	By synthetic ligands/designer drugs	By 1O2
Ligand dependent	Yes	No
Desensitization	Yes	One-off activation
Selectivity	Not activated by endogenous agonists	Double selectivity1
Permanent activation	No	Yes
Apply to multiple GPCR?	Yes	Yes
Allosteric modulation?	No	Possible (positive/negative)

¹Photosensitizer localization/localized light irradiation.

¹O₂: Delta singlet oxygen; DREADD: Designer receptors exclusively activated by designer drugs; GPCR: G protein coupled receptor; GPCR-ABSO: G protein coupled receptor activated by singlet oxygen; RASSL: Receptors activated solely by synthetic ligands.

Table 2 Genetically encoded protein photosensitizers[89-91]

Photosensitiser	Number of amino acid residues	Chromophore	Maximal excitation wavelength (nm)	Maximal emission wavelength (nm)	Quantum yield of 1O2 generation	Fluorescence quantum yield
KillerRed	239	QYG	585	610	0.008	0.25
SuperNova	239	QYG	579	610	0.022	0.30
SuperNovaGreen	239	QWG	440	510	ND	0.23
KillerOrange	239	QWG	512	550	ND	0.42
TagRFP	237	MYG	555	584	0.004	0.48
miniSOG	106	FMN	448	500	0.03	0.45
AsLOV2	175	FMN	448	492	ND	ND
miniSOG2	106	FMN	430	503	ND	ND
Mr4511C71S/G	16	FMN	45	495	0.17/0.1	ND
Pp2FbFPL30M	148	FMN	449	495	0.09	0.25
DsFbFP	138	FMN	449	498	0.33	0.35
EcFbFP	135	FMN	448	496	0.07	0.44
CreiLOV	119	FMN	449	497	0.04	0.32
miniSOGQ103L/V	106	FMN	440	487	0.25/0.39	0.43
SOPP2/3	106	FMN	440	487	0.51/0.61	0.41/0.39
phiSOG	218	FMN	449	498	0.02	0.36
phiSOGQ103V	218	FMN	444	497	0.15	0.35
miniSOGR57Q[89]	106	RF	450	530	0.05/0.07	ND
LovPSO[90]	105	FMN	450	507	0.68	0.27
LovPRO[91]	105	FMN	450	507	0.44	0.34

AsLOV2: Light, oxygen, voltage domain 2 of Aveva sativa; CreiLOV: Light, oxygen, voltage domain of Chlamydomonas reinhardtii; DsFbFP: Flavin-binding fluorescent protein from Dinoroseobacter shibae; EcFbFP: Flavin-binding fluorescent protein from Bacillus subtilis; FMN: Flavin mononucleotide; LovPRO: Light, oxygen, voltage photosensitizer for reactive oxygen species, derived from phototropin 2 of Oryza sativa japanicus; LovPSO: Light, oxygen, voltage photosensitizer for singlet oxygen; miniSOG: Mini singlet oxygen generator; Mr4511^C71S/G: Flavin-binding protein from Methylobacterium radiotolerans, with point mutations of Cys17Ser or Cys17Gly; MYG: Met-Trp-Gly; ND: Not determined; phiSOG: Mini singlet oxygen generator tethered dimer with one monomer having enhanced photostability; PpFbFP: Flavin-binding fluorescent protein from Pseudomonas putida; QWG: Gln-Trp-Gly; QYG: Gln-Tyr-Gly; RF: Riboflavin; SOPP: Singlet oxygen protein photosensitizer. Updated from Li and Cui[36]. Citation: Li Y, Cui ZJ. Photodynamic Activation of Cholecystokinin 1 Receptor with Different Genetically Encoded Protein Photosensitizers and from Varied Subcellular Sites. Biomolecules 2020; 10: 1423. Copyrights© The Authors 2020. Published by MDPI.