SPDP

SPDP most commonly refers to N-succinimidyl 3-(2-pyridyldithio)propionate, a heterobifunctional crosslinker used in bioconjugation. It enables linking of proteins and other biomolecules by providing two reactive ends: an NHS ester for amine targeting and a 2-pyridyldithio group for thiol interactions. The NHS ester reacts with primary amines, such as lysine residues, to form a stable amide bond, attaching the crosslinker to the protein. The 2-pyridyldithio end can undergo disulfide exchange with free thiols, allowing reversible conjugation and forming a new disulfide bond while releasing 2-thiopyridone as a byproduct.

In practice, SPDP is used to create antibody labeling, protein–protein conjugates, or to link enzymes to targeting molecules. It is valued for its cleavable disulfide linkage, which permits controlled release or subsequent modification under reducing conditions. Its use often appears in workflows such as ELISA, Western blotting, and various immunoassays where reversible linkage or residue-specific attachment is advantageous.

Handling considerations include the reactive NHS ester, which necessitates appropriate personal protective equipment and handling in a suitable buffer, typically under cold, dry conditions. SPDP is commonly stored at low temperature (often -20°C) and protected from light to preserve reactivity. While SPDP is the most widely recognized meaning in chemical contexts, the acronym can refer to other entities in different fields; this article focuses on the chemical crosslinker.

See also: heterobifunctional crosslinkers, disulfide-cleavable linkers, protein bioconjugation.