Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, Bethesda, Maryland, USA.
Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, Rockville, Maryland, USA.
J Biol Chem. 2023 Sep;299(9):105099. doi: 10.1016/j.jbc.2023.105099. Epub 2023 Jul 26.
Methionine sulfoxide reductases (MSRs) are key enzymes in the cellular oxidative defense system. Reactive oxygen species oxidize methionine residues to methionine sulfoxide, and the methionine sulfoxide reductases catalyze their reduction back to methionine. We previously identified the cholesterol transport protein STARD3 as an in vivo binding partner of MSRA (methionine sulfoxide reductase A), an enzyme that reduces methionine-S-sulfoxide back to methionine. We hypothesized that STARD3 would also bind the cytotoxic cholesterol hydroperoxides and that its two methionine residues, Met307 and Met427, could be oxidized, thus detoxifying cholesterol hydroperoxide. We now show that in addition to binding MSRA, STARD3 binds all three MSRB (methionine sulfoxide reductase B), enzymes that reduce methionine-R-sulfoxide back to methionine. Using pure 5, 6, and 7 positional isomers of cholesterol hydroperoxide, we found that both Met307 and Met427 on STARD3 are oxidized by 6α-hydroperoxy-3β-hydroxycholest-4-ene (cholesterol-6α-hydroperoxide) and 7α-hydroperoxy-3β-hydroxycholest-5-ene (cholesterol-7α-hydroperoxide). MSRs reduce the methionine sulfoxide back to methionine, restoring the ability of STARD3 to bind cholesterol. Thus, the cyclic oxidation and reduction of methionine residues in STARD3 provides a catalytically efficient mechanism to detoxify cholesterol hydroperoxide during cholesterol transport, protecting membrane contact sites and the entire cell against the toxicity of cholesterol hydroperoxide.
蛋氨酸亚砜还原酶（MSRs）是细胞氧化防御系统中的关键酶。活性氧将蛋氨酸残基氧化为蛋氨酸亚砜，而蛋氨酸亚砜还原酶则催化其还原回蛋氨酸。我们之前鉴定出胆固醇转运蛋白 STARD3 是 MSRA（蛋氨酸亚砜还原酶 A）的体内结合伴侣，MSRA 是一种将蛋氨酸-S-亚砜还原回蛋氨酸的酶。我们假设 STARD3 也会结合细胞毒性胆固醇氢过氧化物，并且其两个蛋氨酸残基 Met307 和 Met427 可能会被氧化，从而解毒胆固醇氢过氧化物。我们现在表明，除了与 MSRA 结合外，STARD3 还与三种 MSRB（蛋氨酸亚砜还原酶 B）结合，这三种酶将蛋氨酸-R-亚砜还原回蛋氨酸。使用纯 5、6 和 7 位位置异构体的胆固醇氢过氧化物，我们发现 STARD3 上的 Met307 和 Met427 都被 6α-过氧-3β-羟基胆甾-4-烯（胆固醇-6α-氢过氧化物）和 7α-过氧-3β-羟基胆甾-5-烯（胆固醇-7α-氢过氧化物）氧化。MSRs 将蛋氨酸亚砜还原回蛋氨酸，恢复 STARD3 结合胆固醇的能力。因此，STARD3 中蛋氨酸残基的循环氧化和还原为胆固醇氢过氧化物在胆固醇转运过程中提供了一种催化有效的解毒机制，保护膜接触位点和整个细胞免受胆固醇氢过氧化物的毒性。
