Comparison List


a.k.a. mEos3d.2G16

mEos4b is a photoconvertible red fluorescent protein published in 2015, derived from Lobophyllia hemprichii. It has moderate acid sensitivity.
Oligomerization Organism Molecular Weight Cofactor
Monomer Lobophyllia hemprichii 25.9 kDa -


State Ex λ Em λ EC (M-1 cm-1) QY Brightness pKa Maturation (min) Lifetime (ns)
Red 570 580 55,500 0.71 39.41 5.8    
Green 505 516 78,170 0.84 65.66 5.5    


From To Switch λ
Green Red 405

mEos4b OSER Measurements

% Normal Cells OSER/NE ratio Cell Type Reference
92.0 ± 2.6 (10000 cells) - HeLa Paez-Segala et al. (2015)


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mEos4b Sequence

mEos4b was derived from mEos3.2 with the following mutations: M1_S2insV/K9R/F34Y/S39T/A69V/C195A



We mutated surface residues on mEos2 to remove nucleophilic groups, which are involved in cross-linking with aldehydes and OsO4. This resulted in the selection of two mutants, mEos4a and mEos4b, each with substantially improved resistance to OsO4 fixation and fluorescence properties unchanged from those of the starting scaffold mEos2. These proteins facilitated the development of two protocols: (i) a ‘consecutive-section’ approach in which adjacent ultrathin sections cut from resin are separately split between PALM imaging and EM fixation and imaging; and (ii) a ‘same-section’ approach, in which a single resin-cut section is subjected to both PALM and TEM and/or SEM. In both cases, plastic resin embedding markedly decreases tissue distortion from dehydration and secondary fixation, and additionally improves performance of the specimen under the electron beam. We also found that this protocol is appropriate for use with HPF-FS (e.g., Fig. 1d) or without it (e.g., Fig. 1e). We found ultrastructure preservation to be comparable between the two.

Kopek et al. (2017)

Osmium-resistant probes for fluorescence and electron microscopy—the fluorescent EosFP derivative mEos4 has recently been described to withstand osmium treatment during EM processing. The mEos4 molecule is therefore still fluorescent in a well-stained resin-embedded sample. In addition, it is compatible with super resolution photoactivated localization microscopy.

Ando et al. (2018)

Primary Reference

Additional References

External Resources

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