Ribosomeinactivatingprotein (RIP) is a toxic protein that acts on rRNA to inhibit ribosome function and is widely distributed in higher plants. Since ricin was first isolated and purified, to the 1990s, ribosome inactivating proteins have been detected in 18 monocotyledonous plants and 122 dicotyledonous plants. Ribosome inactivating proteins are known to be divided into 3 categories. The first type is a single peptide chain protein with a molecular weight of about 30ku, generally a basic glycoprotein, and has RNAN-glycosidase activity. The second type is a heterodimer protein with a molecular weight of about 60ku. The A chain has RNAN-glycosidase activity, and the B chain is a galectin-specific lectin, which can interact with glycoproteins or sugars on the surface of eukaryotic cells. The galactose part of the lipid binds and mediates the reverse entry of the A chain into the cytosol. The third type is rare and is formed by processing of inactive pro-ribosomal inactivating proteins. There is a highly conserved nucleotide domain in the 3 ′ end stem-loop structure of the ribosomal large subunit RNA, namely the S/R domain. The ribosome inactivating protein destroys the ribosomal large subunit by acting on this domain. Base RNA structure, inactivating ribosomes. Ribosome inactivating proteins mainly show RNAN-glycosidase activity and RNA hydrolase activity.
Figure 1. Ribosome-inactivating protein.
Ribosome-inactivating proteins inactivate ribosomes by hydrolyzing bases bound to specific sites on ribosomal RNA, hindering fungal rRNA-mediated protein synthesis and inhibiting fungal growth. In the in vitro antibacterial test, trichosanthin has inhibitory effect on 9 different fungi. Scientists used barley ribosome-inactivating protein to conduct in vitro bacteriostatic tests on 16 species of fungi, and found that only 3 species had a weak inhibitory effect, and 1 species had a strong inhibitory effect. Different fungal ribosomes have different sensitivity to ribosome-inactivating proteins. The ribosome-inactivating protein works synergistically with chitinase, glucanase and the like to enhance the antibacterial ability, because the latter helps the ribosome-inactivating protein to pass through the fungal cell wall. Scientists cloned the structural genes of trichosanthin, tobacco chitinase and tobacco glucanase into prokaryotic expression systems and expressed them respectively. The crude extracts of the prokaryotic expression products of the three genes were used for In vitro antibacterial activity testing, it was found that all three proteins have antifungal activity, and the combination of any two of the three proteins has significantly higher antifungal activity than the activity of a single component. When the three proteins work together, a better antifungal effect is obtained. So far, the role of ribosome-inactivating protein in inhibiting pathogen infection in plants and its role in plant disease resistance expression are unknown. Transforming plants with a ribosome-inactivating protein gene can express resistance to fungal infection.
Ribosome-inactivating proteins have strong broad-spectrum inhibitory effects on animal and plant viruses, and many studies have been used to inactivate HIV and kill tumor cells. For plant viruses, the first to be discovered is that pokeweed antiviral protein has anti-tobacco mosaic virus (TMV) properties. Later, it was discovered that other ribosome-inactivating proteins almost have different degrees of antiviral ability. Regarding the antiviral mechanism of ribosome inactivating protein, there are successively indirect and direct effects. Some ribosome-inactivating proteins exist between the cell wall and the cell membrane and may interact with the virus directly before the virus enters the cell. The effect of certain ribosome-inactivating proteins on the virus is not limited to the inoculation of leaves, but also a systemic inhibitory effect. A variety of plants have been transformed with ribosome-inactivating protein genes from different sources, and the transgenic plants express disease resistance to the virus (Wang et al., 2000).