Sequential ordering among multicolor fluorophores for protein labeling facility via aggregation-elimination based β-lactam probes.

Development of protein labeling techniques with small molecules is enthralling because this method brings promises for triumph over the limitations of fluorescent proteins in live cell imaging. This technology deals with the functionalization of proteins with small molecules and is anticipated to facilitate the expansion of various protein assay methods. A new straightforward aggregation and elimination-based technique for a protein labeling system has been developed with a versatile emissive range of fluorophores. These fluorophores have been applied to show their efficiency for protein labeling by exploiting the same basic principle. A genetically modified version of class A type β-lactamase has been used as the tag protein (BL-tag). The strength of the aggregation interaction between a fluorophore and a quencher plays a governing role in the elimination step of the quencher from the probes, which ultimately controls the swiftness of the protein labeling strategy. Modulation in the elimination process can be accomplished by the variation in the nature of the fluorophore. This diversity facilitates the study of the competitive binding order among the synthesized probes toward the BL-tag labeling method. An aggregation and elimination-based BL-tag technique has been explored to develop an order of color labeling from the equimolar mixture of the labeling probe in solutions. The qualitative and quantitative determination of ordering within the probes toward labeling studies has been executed through SDS-PAGE and time-dependent fluorescence intensity enhancement measurements, respectively. The desirable multiple-wavelength fluorescence labeling probes for the BL-tag technology have been developed and demonstrate broad applicability of this labeling technology to live cell imaging with coumarin and fluorescein derivatives by using confocal microscopy.