Table 1.

Comparison of properties of the photosensory module of BphPs and the GFP-like FPs.

Property	PCM of BphPs	GFP-like FPs	Advantage (+) or Disadvantage (−) of BphPs vs. GFP-like FPs	Ref
Overall structure	Consists of two or three domains with common α/β fold topology linked via α-helixes; exists as monomer, dimer or oligomer	Consist of a single domain, rigid β-barrel formed by 11 β-sheets Exist as monomer, dimer, tetramer or oligomer	(+) Domain organization allow diverse strategies for protein engineering (+) Suitable for engineering of optogenetic tools	4, 7, 28, 29, 32, 33, 39
Size of monomer subunit	PAS-GAF domains: 300–310 a.a. (35–38 kDa) PAS-GAF-PHY domains: 500–530 a.a. (55–60 kDa)	210–240 a.a. (24–28 kDa)	(−) Potentially may affect proper localization or function of target proteins
Chromophore formation	Apoprotein autocatalytically and covalently incorporates BV as a chromophore	Protein folding followed by autocatalytic chromophore formation in presence of oxygen	(+) Does not require molecular oxygen, therefore, may form in anaerobic conditions (−) Require exogenous BV, whose concentration may vary in different cell types and tissues (−) Presence of HO may improve BV incorporation	4, 6, 10–12, 50
Absorbance/Emission maxima	630–750 nm/680–800 nm *	355–635 nm/425–670 nm	(+) Expands GFP-like fluorescent protein palette into NIR region (+) Optimal for whole-body imaging of mammals	2, 4, 10, 20, 23
Photo- convertion wavelength and energy	Red (660–690 nm): 0.05–0.1 J/cm2; Far-red (740–760 nm): 0.025–0.1 J/cm2	Violet-cyan (380–490 nm): up to 180 J/cm2; Orange (560–580 nm): up to 1.6 J/cm2	(+) Easier photoconversion in deep-tissue samples	51–53
Quantum yield	Low	High	(−) Low brightness may limit single- molecule imaging applications	10, 11, 20
Extinction coefficient	High	Moderate	(+) Optimal for optoacoustic imaging (+) Preferable FRET acceptors for red GFP-like FPs	2, 11, 12, 23

^*The upper value of the emission maxima is estimated based on the BphP absorbance spectra.