S-adenosylmethionine stabilizes cystathionine β-synthase and modulates redox capacity
S-adenosylmethionine stabilizes cystathionine β-synthase and modulates redox capacity
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DOI：
10.1073/pnas.0509531103
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发表时间：
2006-04-25
影响因子：
11.1
通讯作者：
Banerjee, R
中科院分区：
文献类型：
--
作者：
Prudova, A;Bauman, Z;Banerjee, R
转硫途径将同型半胱氨酸转化为半胱氨酸，代表抗氧化剂和甲基化代谢之间的代谢联系。该途径的第一步也是关键步骤是由胱硫醚β-合酶 (CBS) 催化，该酶受到复杂的调节，包括甲基供体 S-腺苷甲硫氨酸 (AdoMet) 的变构激活。在这项研究中，我们证明蛋氨酸限制导致 CBS 蛋白质水平下降 > 10 倍，脉冲蛋白水解研究表明，AdoMet 的结合可稳定蛋白质，使其免于降解，稳定程度约为 12 kcal/mol。这些观察结果预测，在 AdoMet 水平降低的病理条件下，CBS 以及谷胱甘肽水平将会降低。事实上，我们在自发性脂肪性肝炎小鼠模型中证明了这一点，其中编码 AdoMet 合成酶的 MAT1A 同工酶基因已被破坏，而在人类肝细胞癌中，MAT1A 被沉默。此外，CBS 水平的降低与用叔丁基氢过氧化物攻击的肝癌细胞的细胞活力降低有关。这项研究揭示了一种机制，通过这种机制，CBS 在正常条件下被 AdoMet 变构激活，但在病理条件下不稳定，从而将代谢流重新导向蛋氨酸保守。这些观察结果解释了氧化还原和甲基化代谢协调变化的机制基础，氧化还原和甲基化代谢是几种复杂疾病的标志。
The transsulfuration pathway converts homocysteine to cysteine and represents the metabolic link between antioxidant and methylation metabolism. The first and committing step in this pathway is catalyzed by cystathionine beta-synthase (CBS), which is subject to complex regulation, including allosteric activation by the methyl donor, S-adenosylmethionine (AdoMet). In this study, we demonstrate that methionine restriction leads to a > 10-fold decrease in CBS protein levels, and pulse proteolysis studies reveal that binding of AdoMet stabilizes the protein against degradation by approximate to 12 kcal/mol. These observations predict that under pathological conditions where AdoMet levels are diminished, CBS, and therefore glutathione levels, will be reduced. Indeed, we demonstrate this to be the case in a mouse model for spontaneous steatolhepatitis in which the gene for the MAT1A isoenzyme encoding AdoMet synthetase has been disrupted, and in human hepatocellular carcinoma, where MAT1A is silenced. Furthermore, diminished CBS levels are associated with reduced cell viability in hepatoma cells challenged with tert-butyl hydroperoxide. This study uncovers a mechanism by which CBS is allosterically activated by AdoMet under normal conditions but is destabilized under pathological conditions, for redirecting the metabolic flux toward methionine conservation. A mechanistic basis for the coordinate changes in redox and methylation metabolism that are a hallmark of several complex diseases is explained by these observations.