Ovothiols are histidine-derived thiols that are receiving a great interest for their biological activities in human model systems. Thanks to the position of the thiol group on the imidazole ring of histidine, these compounds exhibit unusual antioxidant properties. They have been revealing a very promising pharmacological potential due to their anti-proliferative and anti-inflammatory properties, as well as anti-fibrotic activities not always related to their antioxidant power. Ovothiols occur in three differentially methylated forms (A, B and C), isolated from ovary, eggs and biological fluids of many marine invertebrates, mollusks, microalgae, and pathogenic protozoa. These molecules are synthesized by two enzymes: the sulfoxide synthase OvoA and the sulfoxide lyase OvoB. OvoA catalyzes the insertion of the sulfur atom of cysteine on the imidazole ring of histidine, leading to the formation of a sulfoxide intermediate. This is then cleaved by OvoB, giving 5-thiohistidine, finally methylated on the imidazole ring thanks to the methyltransferase domain of OvoA. Recent studies have shown that OvoA homologs are encoded in a wide variety of genomes suggesting that ovothiol biosynthesis is much more widespread in nature than initially thought. Here we have investigated the OvoA occurrence in diatoms, one of the most abundant group of microalgae, dominating marine and freshwater environments. They are considered a very good model system for both biology/photophysiology studies and for biotechnological applications. We have performed comparative sequence and phylogenetic analyses of OvoA from diatoms, highlighting a high degree of conservation of the canonical domain architecture in the analyzed species, as well as a clear clustering of OvoA in the two different morphological groups, i.e. centric and pennate diatoms. The in silico analyses have also revealed that OvoA gene expression is modulated by growth conditions. More importantly, we have characterized the thiol fraction from cultures of the coastal centric diatom Skeletonema marinoi, providing the first evidence of ovothiol B biosynthesis in diatoms.

中文翻译：

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海洋硅藻中卵硫醇生物合成的第一个证据。

卵硫醇是组氨酸衍生的硫醇，由于其在人类模型系统中的生物学活性而引起了极大的兴趣。由于巯基在组氨酸的咪唑环上的位置，这些化合物表现出不同寻常的抗氧化性能。由于它们的抗增殖和抗炎特性，以及抗纤维化活性并不总是与它们的抗氧化能力有关，它们已经显示出非常有希望的药理潜力。卵硫醇以三种差异甲基化形式（A，B和C）存在，它们与许多海洋无脊椎动物，软体动物，微藻类和致病性原生动物的卵巢，卵和生物体液分离。这些分子由两种酶合成：亚砜合酶OvoA和亚砜裂合酶OvoB。OvoA催化半胱氨酸的硫原子在组氨酸的咪唑环上插入，导致形成亚砜中间体。然后通过OvoB裂解，得到5-硫代组氨酸，由于OvoA的甲基转移酶结构域，最终在咪唑环上甲基化。最近的研究表明，OvoA同源物编码在各种各样的基因组中，这表明卵硫醇的生物合成在自然界比最初认为的要广泛得多。在这里，我们研究了在海洋和淡水环境中占主导地位的硅藻（最丰富的微藻群之一）中OvoA的发生。对于生物学/光生理学研究和生物技术应用而言，它们被认为是非常好的模型系统。我们已经对硅藻中的OvoA进行了比较序列和系统发育分析，强调了所分析物种中规范域结构的高度保守性，以及OvoA在两个不同形态组（即中心硅藻和羽状硅藻）中的清晰聚集。电子计算机分析还显示，OvoA基因表达受生长条件调节。更重要的是，我们已经表征了沿海中心硅藻Skeletonema marinoi的培养物中的硫醇部分，为硅藻中硫硫醇B的生物合成提供了第一个证据。