SulfoSMCC

Sulfo-SMCC is a water-soluble, heterobifunctional crosslinker used in bioconjugation to connect primary amines to thiols. It is a sulfo version of SMCC, featuring an N-hydroxysuccinimide (NHS) ester on one end and a maleimide group on the other, linked by a cyclohexane-based spacer. The sulfonate group increases aqueous solubility, enabling reactions in buffered, typically aqueous solutions without organic co-solvents.

Chemistry and mechanism: the NHS ester end reacts with primary amines on proteins or peptides to form a stable amide bond, releasing N-hydroxysuccinimide. The maleimide end conjugates with thiol groups, such as cysteine residues or thiol-modified ligands, to form a stable thioether bond. NHS ester hydrolysis in water competes with amine conjugation, so reaction timing and conditions influence efficiency.

Applications: Sulfo-SMCC is commonly used to attach drugs, fluorophores, or other ligands to antibodies, enzymes, or proteins, enabling antibody-drug conjugates, labeled biomolecules, or surface attachments. It is useful when a primary amine on one partner and a thiol on the other are available, and when aqueous solubility is advantageous.

Considerations: labeling is often not site-specific, since many amines (such as lysines) are present on proteins, which can affect function or binding. Typical conditions involve pH around 7–8 for NHS activation and pH around 6.5–7.5 for thiol coupling. The NHS ester is susceptible to hydrolysis, so timely use and storage are important. The reagent is not cleavable under standard conditions and should be stored frozen and protected from light.

Safety and handling follow standard practices for NHS-ester reagents.