Eos (protein)

Eos (also called EosFP) is a photoactivatable fluorescent protein (PAFP).

Discovery

Eos was isolated from the coral Lobophyllia hemprichii in a large-scale screen for PAFPs.^[1]

Properties

Eos undergoes an irreversible photoconversion in response to 390 nm light. Prior to this conversion, it exhibits a green emission peak at 516 nm. Following conversion, it has a red emission peak at 581 nm.

Wild-type Eos is a tetrameric protein. It has been modified to generate a monomeric form (referred to as mEos) that is more amenable for experiments involving labeling of a single molecule. Further improvements of mEos lead to mEos2 that is able to mature at 37 °C and can be used in mammalian cells.^[2] One drawback of mEos2 - the formation of oligomers at high concentrations - was resolved in the next generation of mEos: mEos3.1 & mEos3.2.^[3]

Properties[4]
Photoconversion wavelength	390 nm
Green absorbance peak	506 nm
Green emission peak	516 nm
Red absorbance peak	571 nm
Red emission peak	581 nm
Green brightness*	1.3X
Red brightness*	0.7X
*Brightness values are relative to EGFP.

Applications

Like other PAFPs, Eos can be used to optically label single cells for subsequent analysis. Because Eos is available in monomeric forms, it can also be used to observe the kinetics and trafficking of single molecules as a fusion protein.

References

1. Wiedenmann et al. 2004. PNAS 101(45), pp 15905-10.
2. McKinney, S. A.; Murphy, C. S.; Hazelwood, K. L.; Davidson, M. W.; Looger, L. L. (2009). "A bright and photostable photoconvertible fluorescent protein". Nature Methods 6 (2): 131–3. doi:10.1038/nmeth.1296. PMC 2745648. PMID 19169260.
3. Zhang, M.; Chang, H.; Zhang, Y.; Yu, J.; Wu, L.; Ji, W.; Chen, J.; Liu, B.; Lu, J.; Liu, Y.; Zhang, J.; Xu, P.; Xu, T. (2012). "Rational design of true monomeric and bright photoactivatable fluorescent proteins". Nature Methods 9 (7): 727–9. doi:10.1038/nmeth.2021. PMID 22581370.
4. Lukyanov et al. 2005. Nature Reviews: Molecular Cell Biology 6(11) pp 885-91.