Fluorescent proteins (FPs) are extremely useful tools for whole-cell, tissue, and animal labeling. For these
purposes, FPs may be monomeric or oligomeric, but should meet the criteria of being tolerated at high expression
levels in cells and having desirable photophysical properties.
Our goal was to create a variant of DsRed-Express that maintains the brightness, fast-maturation, and
photostability of this protein, while exhibiting decreased cytotoxicity. For this purpose, we mutated the surface of
DsRed-Express to decrease aggregation and created DsRed-Express2. DsRed-Express2 retains the favorable
photophysical properties of DsRed-Express while showing dramatically reduced cytotoxicity and higher expression
in bacterial and mammalian systems. Further, it was shown that DsRed-Express2 outperforms other red FPs as a
label for bacterial and mammalian cells.