EZ-Link™ Maleimide Protein Labeling Kit (Thermo Scientific™)

The Thermo Scientific EZ-Link Maleimide Protein Labeling Kit provides a convenient method to label proteins with varying amounts maleimide for crosslinking or conjugation with a thiol/sulfhydryl-containing moiety. Sulfo-SMCC, contained in this kit, readily reacts with the primary amines on a protein to form a covalently attached maleimide group that can be further reacted with a reactive thiol or free cystine to create diverse bioconjugates. This kit contains sufficient reagents for five labeling reactions of up to 100 μL sample with a concentration of 1–10 mg/mL.

Features of the EZ-Link Maleimide Protein Labeling Kit include:
• Heterobifunctional—reactive towards amines and thiols/sulfhydryls
• Soluble—sulfo-SMCC reagent readily dissolves in water
• Stable—cyclohexane bridge confers added stability to the maleimide group making sulfo-SMCC the ideal crosslinking agent for maleimide activation of proteins

Sulfo-SMCC is a heterobifunctional crosslinker that contains a sulfonated N-hydroxysuccinimide (NHS) ester and maleimide group that allow covalent conjugation of amine- and thiol/sulfhydryl-containing molecules. NHS esters react with primary amines at pH 7–9 to form amide bonds, while maleimides react with sulfhydryl groups at pH 6.5–7.5 to form stable thioether bonds. The cyclohexane ring in the spacer arm of sulfo-SMCC decreases the rate of hydrolysis of the maleimide group compared to similar reagents that do not contain this ring. This feature enables proteins that have been maleimide labeled with sulfo-SMCC to be lyophilized and stored for later conjugation to a sulfhydryl-containing molecule.