stapten

Stapten is a term used in chemical biology for small, covalently reactive molecules designed to “staple” two biomolecular partners together. A stapten typically combines two functional modules: a recognition or affinity element that binds to a target molecule (such as a protein) and a latent reactive group that forms a covalent bond with nearby sites once activated. The resulting covalent link stabilizes interactions that may be too transient to detect by noncovalent methods.

Activation of a stapten can be achieved through different triggers. The most common are photochemical, where light activates a reactive moiety to generate a species that forms bonds with adjacent residues or nucleic acids. Widely used photoactivatable groups include diazirines, aryl azides, and psoralen derivatives. Chemical activation is also employed in some designs, using reactive end groups that form covalent bonds under specific conditions or in the presence of catalysts. Some stapten molecules are heterobifunctional crosslinkers that pair a recognition end with a reactive end, enabling crosslinking between two biomolecules or between a biomolecule and a labeled partner.

Applications of stapten reagents focus on capturing and studying transient interactions. They are used in proteomics to map protein–protein or protein–DNA/RNA interactions, in structural biology to stabilize complexes for analysis, and in live-cell or in vitro experiments to profile interaction networks. Common examples include diazirine- or psoralen-based photo-crosslinkers and NHS-ester–diazirine crosslinkers such as Sulfo-SDA.

Limitations include potential nonspecific labeling, dependence on the appropriate activation conditions, and challenges with cellular uptake and cytotoxicity. See also crosslinking reagents, photo-crosslinking, and affinity labeling.