Saxena S K, Rybak S M, Davey R T, Youle R J, Ackerman E J
Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1992 Oct 25;267(30):21982-6.
Angiogenin is a 14.4-kDa human plasma protein with 65% homology to RNase A that retains the key active site residues and three of the four RNase A disulfide bonds. We demonstrate that recombinant angiogenin functions as a cytotoxic tRNA-specific RNase in cell-free lysates and when injected into Xenopus oocytes. Inhibition of protein synthesis by angiogenin correlates with degradation of endogenous oocyte tRNA. Exogenous, radiolabeled tRNA is also hydrolyzed by angiogenin, whereas oocyte rRNA and mRNA are not detectably degraded by angiogenin. Protein synthesis was restored to angiogenin-injected oocytes by injecting the RNase inhibitor RNasin plus total Xenopus or calf liver tRNAs, thereby demonstrating that the tRNA degradation induced by angiogenin was the sole cause of cytotoxicity. A similar tRNA-reversible inhibition of protein synthesis was seen in rabbit reticulocyte lysates. Angiogenin therefore appears to be a specific cellular tRNase, whereas five homologues in the RNase A superfamily lack angiogenin's specificity for tRNA. One of these homologues purified from human eosinophils, eosinophil-derived neurotoxin, nonspecifically degrades oocyte RNA similar to RNase A and is also cytotoxic at very low concentrations.
血管生成素是一种14.4 kDa的人血浆蛋白，与核糖核酸酶A有65%的同源性，保留了关键的活性位点残基和核糖核酸酶A四个二硫键中的三个。我们证明，重组血管生成素在无细胞裂解物中以及注射到非洲爪蟾卵母细胞中时，作为一种细胞毒性tRNA特异性核糖核酸酶发挥作用。血管生成素对蛋白质合成的抑制与内源性卵母细胞tRNA的降解相关。外源性放射性标记的tRNA也会被血管生成素水解，而卵母细胞的rRNA和mRNA不会被血管生成素明显降解。通过注射核糖核酸酶抑制剂核糖核酸酶抑制剂（RNasin）以及非洲爪蟾或小牛肝脏的总tRNA，可使注射了血管生成素的卵母细胞恢复蛋白质合成，从而证明血管生成素诱导的tRNA降解是细胞毒性的唯一原因。在兔网织红细胞裂解物中也观察到了类似的tRNA可逆性蛋白质合成抑制。因此，血管生成素似乎是一种特异性细胞tRNA酶，而核糖核酸酶A超家族中的五个同源物缺乏血管生成素对tRNA的特异性。从人嗜酸性粒细胞中纯化出的其中一种同源物，即嗜酸性粒细胞衍生的神经毒素，会像核糖核酸酶A一样非特异性地降解卵母细胞RNA，并在极低浓度下也具有细胞毒性。
