Saporin

Saporin is a ribosome-inactivating protein (RIP) found in the plant Saponaria officinalis, commonly known as soapwort. It is a single-chain protein with a molecular weight of approximately 30 kDa and belongs to the type 1 RIP family.

Saporin functions by catalytically cleaving an N-glycosidic bond of a specific adenine residue in the universally conserved α-sarcin/ricin loop (SRL) of 28S ribosomal RNA (rRNA). This modification irreversibly inhibits protein synthesis, leading to cell death. Unlike type 2 RIPs such as ricin, saporin lacks a cell-binding domain. Consequently, saporin itself exhibits relatively low cytotoxicity unless delivered intracellularly.

Due to its potent and irreversible inhibition of protein synthesis and its lack of a cell-binding domain, saporin is widely used in the construction of immunotoxins and other targeted toxins. These constructs utilize antibodies, growth factors, peptides, or other targeting moieties conjugated to saporin to selectively deliver the toxin to specific cell populations. This targeted delivery mechanism allows for the selective elimination of specific cells, such as cancer cells, without causing widespread toxicity.

Saporin conjugates are used extensively in research for applications such as lesioning specific neuronal populations in the brain, eliminating specific immune cells, and targeting cancer cells in vitro and in vivo. The efficiency and specificity of saporin-based targeted toxins depend on the affinity and specificity of the targeting moiety, as well as the method of conjugation.