title: Selective and Efficient Cysteine Conjugation by Maleimides in the Presence of Phosphine Reductants.
abstract: Sulfhydryl functions of thiol-containing amino acids are prime attachment sites for conjugation of labels, ligands, or drugs to proteinaceous compounds. Usually the thiol is offered a xenobiotic electrophilic moiety from the molecule to be attached such as a maleimido function. As sulfhydryls tend to oxidize into disulfides they must be reduced before conjugation. A popular thiol reduction reagent in biosciences is the substituted phosphine tris(2-carboxyethyl)phosphine (TCEP). Yet, phosphines are nucleophilic, too, and thus potentially compete with thiols for the electron-poor alkene moiety of maleimide resulting in complex product mixtures. To overcome this shortcoming we developed a method to eliminate excess reducing agent in the reaction mixture by selective oxidation of the phosphine with azidobenzoic acid before coupling. This results in a selective and efficient labeling of cysteines by maleimides.
authors.affiliation: Division of Mucosal Immunology & Diagnostics, Priority Area Asthma & Allergy, Research Center Borstel, Airway Research Center North (ARCN), Member of the German Center for Lung Research (DZL) , 23845 Borstel, Germany.
authors.forename: Maik
authors.initials: M
authors.lastname: Henkel
authors.affiliation: Division of Mucosal Immunology & Diagnostics, Priority Area Asthma & Allergy, Research Center Borstel, Airway Research Center North (ARCN), Member of the German Center for Lung Research (DZL) , 23845 Borstel, Germany.
authors.forename: Niels
authors.initials: N
authors.lastname: Röckendorf
authors.affiliation: Division of Mucosal Immunology & Diagnostics, Priority Area Asthma & Allergy, Research Center Borstel, Airway Research Center North (ARCN), Member of the German Center for Lung Research (DZL) , 23845 Borstel, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Frey
mesh_terms: D003545:Cysteine / Q000737:chemistry*; D008301:Maleimides / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry; D010720:Phosphines / Q000737:chemistry; D019163:Reducing Agents / Q000737:chemistry; D013451:Sulfonic Acids / Q000737:chemistry
chemical_list: D003545:Cysteine; D008301:Maleimides; D009943:Organophosphorus Compounds; D010720:Phosphines; D019163:Reducing Agents; D013451:Sulfonic Acids; C400058:triphenylphosphine-3,3',3''-trisulfonic acid; C080938:tris(2-carboxyethyl)phosphine; C044646:phosphine