摘要
核糖体失活蛋白是一类作用于rRNA而抑制核糖体功能的毒蛋白,广泛存在于高等植物体内。核糖体失活蛋白分为3类:第1类是单肽链蛋白,分子量大约30kD,一般为碱性糖蛋白,具有RNAN-糖苷酶活性;第2种类型是异源二聚体蛋白,分子量大约为60kD,A链具有RNAN-糖苷酶活性,B链是一个对半乳糖专一的凝集素,B链可以分别或同时与真核细胞表面的糖蛋白或糖脂的半乳糖部分结合,介导A链逆向进入胞质溶胶;第3种类型是先合成无活性的核糖体失活蛋白前体,然后在涉及形成活性位点的氨基酸之间进行酶解加工。核糖体失活蛋白通过对核糖体大亚基RNA的3'端茎环结构中一个高度保守的核苷酸区域的作用,破坏核糖体大亚基RNA的结构,使核糖体失活。核糖体失活蛋白的功能主要通过2个方面产生,即RNA的N-糖苷酶活性和RNA水解酶的活性。核糖体失活蛋白不仅对病毒具有广谱抗性,而且对真菌和昆虫也有抗性。核糖体失活蛋白可以给植物提供对病毒和真菌的广谱抗性,这为我们利用有关的核糖体失活蛋白基因提高植物对病毒和真菌的抗性提供了一条新的途径。
Ribosome-inactivating protein (RIP) is a group of toxic proteins inhibiting prokaryotic and eukaryotic ribosome by a specific modification of the large rRNA. It exists popularly in high plants with functions of anti-tumour, anti-virus and anti-fungus. RIPs are classified into three groups based on their physical properties. Type 1 RIPs, are monomeric enzymes, each with an approximate molecular weight of 30kD. They are basic proteins. Most RIPs that have been characterized fall into the type 1 class. Type 2 RIPs, are highly toxic heterodimeric proteins with enzymatic and lectin properties in separate polypeptide subunits, with approximate molecular weight of 60kD. One polypeptide with RIP activity (A-chain) is linked to a galactose binding lectin (B-chain) through a disulfide bond. The lectin chain can bind to galactosyl moieties of glycoproteins and/or glycolipids found on the surface of eukaryotic cells and mediate retrograde transport of the A-chain to the cytosol. Type 3 RIPs are synthesized as inactive precursors (proRIPs) that require proteolytic processing events to occur between amino acids involved in formation of the active site. The enzymatic activity of RIPs was an N-glycosidation to remove a specific adenine corresponding to residue A4324 in rat 28S rRNA. This adenine lies within a 14-nucleotide region that is known as the ?-sarcin loop and is conserved in large rRNAs from bacteria to humans. Expression of RIPs genes can offer transgenic plants broad spectrum resistance to viruses and fungi. This is probably a new way to develop disease-resistant crop varieties.
出处
《分子植物育种》
CAS
CSCD
2005年第4期566-570,共5页
Molecular Plant Breeding
