Ribosome-inactivating protein

Ribosome-inactivating protein
Structure of pokeweed antiviral protein.[1]
Identifiers
Symbol	RIP
Pfam	PF00161
InterPro	IPR001574
PROSITE	PDOC00248
SCOP2	1paf / SCOPe / SUPFAM
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary PDB PDB: 1abr​ PDB: 1aha​ PDB: 1ahb​ PDB: 1ahc​ PDB: 1apa​ PDB: 1apg​ PDB: 1br5​ PDB: 1br6​ PDB: 1bry​ PDB: 1cf5​

A ribosome-inactivating protein (RIP) is a protein synthesis inhibitor that acts at the eukaryotic ribosome.^[2] This protein family describes a large family of such proteins that work by acting as rRNA N-glycosylase (EC 3.2.2.22). They inactivate 60S ribosomal subunits by an N-glycosidic cleavage, which releases a specific adenine base from the sugar-phosphate backbone of 28S rRNA.^[3][4][5] RIPs exist in bacteria and plants.^[6]

Members of the family include shiga toxins, and type I (e.g. trichosanthin and luffin) and type II (e.g. ricin, agglutinin, and abrin) ribosome inactivating proteins (RIPs). All these toxins are structurally related. RIPs have been of considerable interest because of their potential use, conjugated with monoclonal antibodies, as immunotoxins to treat cancers. Further, trichosanthin has been shown to have potent activity against HIV-1-infected T cells and macrophages.^[7] Elucidation of the structure-function relationships of RIPs has therefore become a major research effort. It is now known that RIPs are structurally related. A conserved glutamic residue has been implicated in the catalytic mechanism;^[8] this lies near a conserved arginine residue, which also plays a role in catalysis.^[9]

Only a minority of RIPs are toxic to humans when consumed, and proteins of this family are found in the vast majority of plants used for human consumption, such as Rice, Maize and Barley. In plants, they are thought to defend against pathogens and insects.^[10]