Atto 550 Protein Labeling Kit

Fluorescence techniques have become a major tool in biological sciences. Fluorescent proteins such as GFP and DsRed fused to the protein of interest (POI) allow expression analysis and in vivo protein localization. Their application however, is limited due to the large molecular weight of those fusion proteins. Furthermore, the associated molecular biology is tedious and time-consuming. Small fluorophores, covalently attached to the POI, may help to overcome this problem. The most common labeling method for proteins is amine modification. Amine-reactive fluorophores such as NHS-esters readily react with lysines, present at the surface of the POI, resulting in a stable covalent bond. (Please note: Jena Bioscience offers a ready-to-use kit for labeling of lysine residues with high-quality small fluorophores (Cat.# FP-201) for application in immunochemistry and other assays that require extraordinary stability of the conjugate). Although fluorescent labeling of lysine residues is a reliable method, the alternative labeling of the thiol group of cysteines is often preferred for investigating structure, function and interactions of the POI. Since many enzymes contain a cysteine in their catalytic domain, protein activity and function may be conveniently investigated by targeting cysteines involved in the catalytic process or binding site.[1,2] In general, thiol labeling is more specific than amine labeling due to the relatively low abundance of cysteines compared to lysines. Since however, appearance of cysteines and lysines varies among different proteins, the amino acid sequence and tertiary structure of the POI must be analyzed prior to deciding on the labeling strategy. This Jena Bioscience Protein Labeling Kit is designed for labeling the cysteines of a POI with a small fluorophore resulting in a fluorescent protein-fluorophore conjugate. It contains all reagents required for performing 3 separate labeling reactions of 1 mg of POI.