Gold fluorescent annexin A5 as a novel apoptosis detection tool

We describe a golden fluorescent apoptosis detection tool, which we generated by a fusion of golden fluorescent protein (GdFP) with human annexin A5 (anxA5). GdFP was obtained by replacement of tryptophan at position 66 with 4-aminotryptophan in the chromophore of enhanced cyan fluorescent protein. The GdFP-anxA5 construct combines highly desirable features originating from both fusion partners. These include (i) strong binding to membrane phosphatidylserine patches of apoptotic cells in the presence of Ca²⁺ which is brought about by anxA5, (ii) the stable and homogeneous monomeric state, (iii) as well as the red-shifted fluorescence maximum at 574 nm originating from GdFP. We found that GdFP-anxA5 is equally well applicable for apoptosis studies as a routinely used fluorescein 5′-isothiocyanate-annexin A5 conjugate. Golden fluorescent annexin A5 represents a new, stable, and homogeneous red-shifted optical probe for the efficient detection of apoptosis by fluorescence microscopy or by flow cytometry.