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Reference.org
Ribosome-inactivating protein
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<p>A ribosome-inactivating protein (RIP) is a <a href="/facts/Protein_synthesis_inhibitor/MNmKF8Mu">protein synthesis inhibitor</a> that acts at the <a href="/facts/Eukaryote/SkwyPLMA">eukaryotic</a> <a href="/facts/Ribosome/CF2u2gtg">ribosome</a>. This <a href="/facts/Protein_family/EHt5xwCA">protein family</a> describes a large family of such proteins that work by acting as <a href="/facts/RRNA_N-glycosylase/cTqs4FGL">rRNA N-glycosylase</a> (EC 3.2.2.22). They inactivate 60S ribosomal subunits by an N-glycosidic cleavage, which releases a specific <a href="/facts/Adenine/PSeDFBnl">adenine</a> base from the sugar-phosphate backbone of 28S <a href="/facts/RRNA/zy5FxddY">rRNA</a>. RIPs exist in bacteria and plants. </p><p>Members of the family include <a href="/facts/Shiga_toxin/9ST35CLn">shiga toxins</a>, and type I (e.g. <a href="/facts/Trichosanthin/3mJ6UCxt">trichosanthin</a> and luffin) and type II (e.g. <a href="/facts/Ricin/6R9wsnRc">ricin</a>, <a href="/facts/Agglutinin/lteb7CjA">agglutinin</a>, and <a href="/facts/Abrin/QzstP0w9">abrin</a>) ribosome inactivating proteins (RIPs). All these toxins are structurally related. RIPs have been of considerable interest because of their potential use, conjugated with <a href="/facts/Monoclonal_antibody/4rUBWB87">monoclonal antibodies</a>, as <a href="/facts/Immunotoxin/Hy1l82K1">immunotoxins</a> to treat cancers. Further, <a href="/facts/Trichosanthin/3mJ6UCxt">trichosanthin</a> has been shown to have potent activity against <a href="/facts/HIV-1/vzeVgtKQ">HIV-1</a>-infected <a href="/facts/T_cells/5z6PQ9UN">T cells</a> and <a href="/facts/Macrophage/z7hkQu3o">macrophages</a>. 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; this lies near a conserved <a href="/facts/Arginine/y49Hdf1e">arginine</a> residue, which also plays a role in catalysis. </p><p>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. </p>