Ribosome-inactivating protein

PDB 1paf EBI

Ribosome-inactivating protein (RIP) is a type of protein that inhibits protein synthesis by inactivating the ribosome. These proteins are found in a variety of plants, bacteria, and fungi. RIPs are classified into two main types: Type I and Type II.

Types of Ribosome-inactivating Proteins

Type I RIPs

Type I RIPs consist of a single polypeptide chain that possesses N-glycosidase activity. This activity allows the protein to remove a specific adenine base from the 28S ribosomal RNA, which is a crucial component of the ribosome's peptidyl transferase center. Examples of Type I RIPs include saporin and pokeweed antiviral protein.

Type II RIPs

Type II RIPs are composed of two polypeptide chains: an A-chain and a B-chain. The A-chain has the same enzymatic activity as Type I RIPs, while the B-chain facilitates the entry of the A-chain into the cell by binding to specific cell surface receptors. Notable examples of Type II RIPs include ricin and abrin.

Mechanism of Action

RIPs exert their toxic effects by depurinating a specific adenine residue in the 28S rRNA of the 60S ribosomal subunit. This depurination event disrupts the ribosome's ability to interact with elongation factors, thereby halting protein synthesis. The inhibition of protein synthesis ultimately leads to cell death.

Biological Functions

RIPs are believed to play a role in the plant defense mechanisms against herbivores and pathogens. They may also have antiviral and antifungal properties. In some cases, RIPs have been studied for their potential use in cancer therapy due to their ability to selectively target and kill cancer cells.

Applications

RIPs have been explored for various applications in biotechnology and medicine. For instance, they have been used in the development of immunotoxins for targeted cancer therapy. Additionally, RIPs have been investigated for their potential use in agriculture as natural pesticides.

Safety and Toxicity

While RIPs have potential therapeutic applications, they are also highly toxic. For example, ricin, a Type II RIP, is one of the most potent toxins known. Therefore, the use of RIPs in medical and agricultural applications requires careful handling and thorough safety evaluations.

Related Pages

• Ribosome
• Protein synthesis
• Ricin
• Abrin
• Saporin
• Pokeweed antiviral protein
• N-glycosidase
• 28S ribosomal RNA
• Peptidyl transferase
• Cell death
• Plant defense