Park M H, Wolff E C, Folk J E
Enzyme Chemistry Section, National Institute of Dental Research, NIH, Bethesda, MD 20892.
Biofactors. 1993 May;4(2):95-104.
The amino acid, hypusine [N epsilon-(4-amino-2-hydroxybutyl) lysine], a unique component of one cellular protein, eukaryotic translation initiation factor 5A (eIF-5A, old terminology eIF-4D), is formed post-translationally in two enzymatic steps: (i) transfer of the 4-aminobutyl moiety of the polyamine spermidine to the epsilon-amino group of a single specific lysine residue in the eIF-5A precursor protein to form an intermediate, deoxyhypusine, and (ii) subsequent hydroxylation in this 4-aminobutyl portion. Hypusine is produced soon after the translation of eIF-5A mRNA; the modification is essentially irreversible. Hypusine is found in all eukaryotes examined as well as in archaebacteria; it does not occur in eubacteria. The protein containing hypusine from each species displays a high degree of amino acid identity; the sequence of amino acids surrounding the hypusine residue is strictly conserved, suggesting the importance of the hypusine modification throughout evolution. Expression of one of the two yeast eIF-5A genes is required for survival and the lysine codon at the site of hypusine synthesis is vital for yeast growth. The precise cellular function of eIF-5A remains to be elucidated; however, eIF-5A stimulates methionyl-puromycin synthesis in a model assay for translation initiation and eIF-5A precursors containing lysine in place of hypusine are inactive in this assay. This provides evidence that the hypusine modification is needed for eIF-5A activity. In view of the important role of hypusine in eIF-5A and because of the narrow specificities of the enzymes involved in formation of this unusual amino acid, the hypusine biosynthetic steps offer promising targets for intervention in cellular proliferation. Spermidine analogs that are inhibitors of deoxyhypusine synthase in vitro also cause inhibition of hypusine formation in cells, together with a reduction in protein synthesis and in cell growth. In addition, certain metal chelating inhibitors of deoxyhypusine hydroxylase exhibit anti-proliferative effects by arresting mammalian cells at the G1/S boundary of the cell cycle. These results lay the foundation for the potential regulation of cellular events through the application of specific and potent inhibitors of hypusine biosynthesis.
氨基酸hypusine（Nε-（4-氨基-2-羟基丁基）赖氨酸）是一种细胞蛋白质——真核生物翻译起始因子5A（eIF-5A，旧称eIF-4D）的独特组成成分，它在翻译后通过两个酶促步骤形成：（i）多胺亚精胺的4-氨基丁基部分转移至eIF-5A前体蛋白中单个特定赖氨酸残基的ε-氨基上，形成中间体脱氧hypusine；（ii）随后该4-氨基丁基部分发生羟基化。Hypusine在eIF-5A mRNA翻译后不久产生；这种修饰基本上是不可逆的。在所有已检测的真核生物以及古细菌中都发现了hypusine；它在真细菌中不存在。来自每个物种的含hypusine的蛋白质都显示出高度的氨基酸同一性；hypusine残基周围的氨基酸序列严格保守，这表明hypusine修饰在整个进化过程中都很重要。酵母的两个eIF-5A基因之一的表达是生存所必需的，并且hypusine合成位点处的赖氨酸密码子对酵母生长至关重要。eIF-5A的确切细胞功能仍有待阐明；然而，在翻译起始的模型检测中，eIF-5A能刺激甲硫氨酰-嘌呤霉素的合成，而含有赖氨酸而非hypusine的eIF-5A前体在该检测中无活性。这提供了证据表明hypusine修饰是eIF-5A活性所必需的。鉴于hypusine在eIF-5A中的重要作用，并且由于参与形成这种不寻常氨基酸的酶的特异性狭窄，hypusine生物合成步骤为干预细胞增殖提供了有前景的靶点。在体外作为脱氧hypusine合酶抑制剂的亚精胺类似物也会导致细胞中hypusine形成受到抑制，同时蛋白质合成和细胞生长减少。此外，某些脱氧hypusine羟化酶的金属螯合抑制剂通过使哺乳动物细胞停滞在细胞周期的G1/S边界而表现出抗增殖作用。这些结果为通过应用hypusine生物合成的特异性强效抑制剂来潜在调节细胞事件奠定了基础。
