Reagents and a method for saturation labelling of proteins

Abstract

A matched set of fluorescent dyes is provided, wherein each dye of the set is capable of covalent attachment to a protein and wherein each of the dyes has a molecular structure and a charge that is matched one with the other, such that relative electrophoretic mobility of a protein labeled with one dye of the set is the same as the electrophoretic mobility of the protein labeled with a different dye of the set. The matched set comprises at least two different fluorescent dyes of formula: wherein n is 1, 2, or 3; Zand Zindependently represent the carbon atoms necessary to complete a phenyl or naphthyl ring system; one of groups Rand Ris a target bonding group; remaining group Ror Ris selected from —(CH)—W or —(CH)—H; group Ris hydrogen, except when either Ror Ris —(CH)—H, in which case Ris W; and W is selected from sulphonic acid and sulphonate. The invention also provides a method for saturation labeling of a protein with a fluorescent dye so as to label all available target amino acid, suitably cysteine, residues in the protein, thereby giving a single population of labeled protein molecules.