In the recent paper on the new Zoanthus derived fluorescent protein, mPapaya1 , I saw a figure in the supplementary material that gives a good illustration of the challenges comparing photobleaching rates between proteins The figure is reproduced here:It’s hard to compare between the mPapaya and mCitrine / mVenus proteins because different filters were used in each panel, but mCitrine / mVenus can be compared and mPapaya1 / 0.6 can be compared. mCitrine and mVenus behave the same under all illumination conditions, with mVenus slightly more photostable, but the photostability of the mPapayas vary depending under illumination conditions. Under mercury arc lamp illumination mPapaya0.6 and mPapaya1 are about equally photostable, but under LED or laser illumination mPapaya1 is substantially more photostable.
There are a number of reasons that there may be this difference in bleaching rates (excitation wavelength and peak intensity come immediately to mind) but what it does clearly show is the difficulty in coming up with a global ranking of photostability of proteins. If the relative photostability of proteins depends on the conditions they are measured under, then you need to specify the measurement conditions to know the relevant bleaching rate. If you’re trying to compile data for many proteins from many different papers (like we are), then saying something sensible about relative photostability becomes very challenging.
- H. Hoi, E. Howe, Y. Ding, W. Zhang, M. Baird, B. Sell, J. Allen, M. Davidson, and R. Campbell, "An Engineered Monomeric Zoanthus sp. Yellow Fluorescent Protein", Chemistry & Biology, vol. 20, pp. 1296-1304, 2013. http://dx.doi.org/10.1016/j.chembiol.2013.08.008