Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th Street, Miami, FL 33199, United States.
Department of Biochemistry, 89 Beaumont Ave, Given Building Room 413B, Burlington, VT 05405, United States.
Comp Biochem Physiol C Toxicol Pharmacol. 2019 Mar;217:76-86. doi: 10.1016/j.cbpc.2018.11.015. Epub 2018 Nov 23.
The activities of two effectors, brevetoxin (PbTx) and manumycin-A (Man-A), of thioredoxin reductase (TrxR) have been evaluated against a series of fourteen TrxR orthologs originating from mammals, insects and protists and several mutants. Man-A, a molecule with numerous electrophilic sites, forms a covalent adduct with most selenocystine (Sec)-containing TrxR enzymes. The evidence also demonstrates that Man-A can form covalent adducts with some non-Sec-containing enzymes. The activities of TrxR enzymes towards various substrates are moderated by Man-A either positively or negatively depending on the enzyme. In general, the reduction of substrates by Sec-containing TrxR is inhibited and NADPH oxidase activity is activated. For non-Sec-containing TrxR the effect of Man-A on the reduction of substrates is variable, but NADPH oxidase activity can be activated even in the absence of covalent modification of TrxR. The effect of PbTx is less pronounced. A smaller subset of enzymes is affected by PbTx. With a single exception, the activities of most of this subset are activated. Although both PbTx variants can react with selenocysteine, a stable covalent adduct is not formed with any of the TrxR enzymes. The key findings from this work are (i) the identification of an alternate mechanism of toxicity for the algal toxin brevetoxin (ii) the demonstration that covalent modification of TrxR is not a prerequisite for the activation of NADPH oxidase activity of TrxR and (iii) the identification of an inhibitor which can discriminate between cytosolic and mitochondrial TrxR.
已评估硫氧还蛋白还原酶 (TrxR) 的两种效应物——布雷菲德菌素 (PbTx) 和马努菌素 A (Man-A) 对来自哺乳动物、昆虫和原生动物的十四种 TrxR 同源物以及几种突变体的活性。Man-A 是一种具有多个亲电位点的分子，与大多数含有硒代半胱氨酸 (Sec) 的 TrxR 酶形成共价加合物。证据还表明，Man-A 可以与一些不含 Sec 的酶形成共价加合物。根据酶的不同，Man-A 可正面或负面调节 TrxR 酶对各种底物的活性。一般来说，含 Sec 的 TrxR 对底物的还原被抑制，NADPH 氧化酶活性被激活。对于不含 Sec 的 TrxR，Man-A 对底物还原的影响是可变的，但即使没有 TrxR 的共价修饰，NADPH 氧化酶活性也可以被激活。PbTx 的作用则不那么明显。一小部分酶受 PbTx 影响。除了一个例外，这个子集的大多数酶的活性都被激活。尽管两种 PbTx 变体都可以与硒代半胱氨酸反应，但与任何一种 TrxR 酶都没有形成稳定的共价加合物。这项工作的主要发现是：(i) 鉴定出藻类毒素布雷菲德菌素 (PbTx) 的另一种毒性作用机制；(ii) 证明 TrxR 的共价修饰不是激活 TrxR 的 NADPH 氧化酶活性的先决条件；(iii) 鉴定出一种可以区分细胞质和线粒体 TrxR 的抑制剂。
