Masip M, Lacadena J, Mancheño J M, Oñaderra M, Martínez-Ruiz A, Martínez del Pozo A, Gavilanes J G
Departamento de Bioquímica y Biología Molecular, Facultad de Química, Universidad Complutense, Madrid, Spain.
Eur J Biochem. 2001 Dec;268(23):6190-6. doi: 10.1046/j.0014-2956.2001.02566.x.
Alpha-sarcin, a cyclizing ribonuclease secreted by the mould Aspergillus giganteus, is one of the best characterized members of a family of fungal ribotoxins. This protein induces apoptosis in tumour cells due to its highly specific activity on ribosomes. Fungal ribotoxins display a three-dimensional protein fold similar to those of a larger group of microbial noncytotoxic RNases, represented by RNases T1 and U2. This similarity involves the three catalytic residues and also the Arg121 residue, whose counterpart in RNase T1, Arg77, is located in the vicinity of the substrate phosphate moiety although its potential functional role is not known. In this work, Arg121 of alpha-sarcin has been replaced by Gln or Lys. These two mutations do not modify the conformation of the protein but abolish the ribosome-inactivating activity of alpha-sarcin. In addition, the loss of the positive charge at that position produces dramatic changes on the interaction of alpha-sarcin with phospholipid membranes. It is concluded that Arg121 is a crucial residue for the characteristic cytotoxicity of alpha-sarcin and presumably of the other fungal ribotoxins.
α-肌动蛋白是由巨大曲霉分泌的一种环化核糖核酸酶，是真菌核糖体毒素家族中特征最明确的成员之一。这种蛋白质由于其对核糖体的高度特异性活性而诱导肿瘤细胞凋亡。真菌核糖体毒素呈现出一种三维蛋白质折叠结构，类似于以核糖核酸酶T1和U2为代表的一大类微生物非细胞毒性核糖核酸酶。这种相似性涉及三个催化残基以及精氨酸121残基，核糖核酸酶T1中的对应残基精氨酸77位于底物磷酸部分附近，尽管其潜在功能作用尚不清楚。在这项工作中，α-肌动蛋白的精氨酸121已被谷氨酰胺或赖氨酸取代。这两种突变不会改变蛋白质的构象，但会消除α-肌动蛋白的核糖体失活活性。此外，该位置正电荷的丧失会使α-肌动蛋白与磷脂膜的相互作用发生显著变化。得出的结论是，精氨酸121是α-肌动蛋白以及可能其他真菌核糖体毒素特征性细胞毒性的关键残基。
