Primitive sterol evolution plays an important role in fossil record interpretation and offers potential therapeutic avenues for human disease resulting from nematode infections. Recognizing that C4-methyl stenol products [8(14)-lophenol] can be synthesized in bacteria while C4-methyl stanol products (dinosterol) can be synthesized in dinoflagellates and preserved as sterane biomarkers in ancient sedimentary rock is key to eukaryotic sterol evolution. In this regard, nematodes have been proposed to convert dietary cholesterol to 8(14)-lophenol by a secondary metabolism pathway that could involve sterol C4 methylation analogous to the C2 methylation of hopanoids (radicle-type mechanism) or C24 methylation of sterols (carbocation-type mechanism). Here, we characterized dichotomous cholesterol metabolic pathways in Caenorhabditis elegans that generate 3-oxo sterol intermediates in separate paths to lophanol (4-methyl stanol) and 8(14)-lophenol (4-methyl stenol). We uncovered alternate C3-sterol oxidation and Δ⁷ desaturation steps that regulate sterol flux from which branching metabolite networks arise, while lophanol/8(14)-lophenol formation is shown to be dependent on a sterol C4α-methyltransferse (4-SMT) that requires 3-oxo sterol substrates and catalyzes a newly discovered 3-keto-enol tautomerism mechanism linked to S-adenosyl-l-methionine-dependent methylation. Alignment-specific substrate-binding domains similarly conserved in 4-SMT and 24-SMT enzymes, despite minimal amino acid sequence identity, suggests divergence from a common, primordial ancestor in the evolution of methyl sterols. The combination of these results provides evolutionary leads to sterol diversity and points to cryptic C4-methyl steroidogenic pathways of targeted convergence that mediate lineage-specific adaptations.-.

中文翻译：

---

线虫固醇C4α-甲基转移酶催化引起固醇多样性的新甲基化反应。

原始固醇的进化在化石记录解释中起着重要作用，并为线虫感染导致的人类疾病提供了潜在的治疗途径。认识到C4-甲基甾醇产品[8（14）-lophenol]可以在细菌中合成，而C4-甲基甾烷醇产品（地甾醇）可以在壬鞭毛虫中合成并保存为古代沉积岩中的甾烷生物标志物，这是真核固醇进化的关键。在这方面，已提出线虫通过次级代谢途径将饮食中的胆固醇转化为8（14）-氯酚，该途径可能涉及类似于类hop烷的C2甲基化（自由基型机制）或甾醇的C24甲基化（碳酸化）的甾醇C4甲基化。型机制）。在这里，我们表征了二分胆固醇代谢途径秀丽隐杆线虫在分开的途径中生成3-氧代固醇中间体，以生成番phan醇（4-甲基甾烷醇）和8（14）-间苯酚（4-甲基甾醇）。我们发现备用C3-固醇氧化和Δ ⁷调节从该分支代谢网络出现固醇去饱和磁通步骤，而lophanol / 8（14）形成-lophenol示出依赖于固醇C4α-methyltransferse（4- SMT），该需要3-氧代固醇底物并催化新发现的与S连接的3-酮-烯醇互变异构机理-腺苷-1-蛋氨酸依赖性甲基化。尽管氨基酸序列的同一性最低，但比对特异性底物结合结构域在4-SMT和24-SMT酶中同样保守，表明在甲基固醇的进化中与普通的原始祖先不同。这些结果的组合提供了导致固醇多样性的进化结果，并指出了定向收敛的隐秘C4-甲基类固醇生成途径，该途径介导了谱系特异性适应。