Saporin

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Function

Saporin is a ribosome-inactivating protein (RIP); alone, saporin does not selectively inactive ribosomes but rather conjugate with other molecules like peptides ^[3]. Saponaria officinalis is the plant from which saporin is extracted ^[4]. Type I and type II RIPS exist. Of these types, saporin is a type I. Ribosome inactivating proteins catalyze a cleavages N-glycosidic bond that is formed between the ribosome and adenine ^[5]. This adenine has the role of binding EF-1 and EF-2 to a ribosome ^[5]. EF stands for elongation factor. Since adenine no longer has a bond to the ribosome, the elongation step in translation cannot occur because the elongation factors cannot bind to just the ribosome. The specific elongation factor that is inhibited is elongation factor 2, which causes irreversible damage and disallows protein synthesis ^[4].

Disease

Relevance

Structural highlights

Type 1 RIPS are monomeric, meaning they have one part ^[6]. Saporin-S6 at maturity is 256 amino acids long ^[4]. While saporin consists of different residues and molecules, there is only one Chain A in it, and thus is monomeric. Chain A is a polypeptide weighing 30 KDa ^[7]. This chain consists of beta-sheets and alpha-helixes. The β-sheets make up the N-terminal domain, while the 𝛼-helix portion is the C-terminal domain ^[5]. In the figure of Chain A, the 𝛼-helices are spiral-shaped strands, while the β-sheets are more of a flat strand.

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