Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States.
Biochemistry. 2021 Nov 16;60(45):3347-3361. doi: 10.1021/acs.biochem.1c00469. Epub 2021 Nov 3.
Ribosomally synthesized post-translationally modified peptides (RiPPs) are ubiquitous and represent a structurally diverse class of natural products. The ribosomally encoded precursor polypeptides are often extensively modified post-translationally by enzymes that are encoded by coclustered genes. Radical -adenosyl-l-methionine (SAM) enzymes catalyze numerous chemically challenging transformations. In RiPP biosynthetic pathways, these transformations include the formation of C-H, C-C, C-S, and C-O linkages. In this paper, we show that the gene encodes a radical SAM protein, SbtM, which catalyzes the cyclization of a Cys/SeCys residue in a minimal peptide substrate. Biochemical studies of this transformation support a mechanism involving H-atom abstraction at the C-3 of the substrate Cys to initiate the chemistry. Several possible cyclization products were considered. The collective biochemical, spectroscopic, mass spectral, and computational observations point to a thiooxazole as the product of the SbtM-catalyzed modification. To our knowledge, this is the first example of a radical SAM enzyme that catalyzes a transformation involving a SeCys-containing peptide and represents a new paradigm for formation of oxazole-containing RiPP natural products.
核糖体合成的翻译后修饰肽（RiPPs）无处不在，代表了一类结构多样的天然产物。核糖体编码的前体多肽通常通过由共聚类基因编码的酶进行广泛的翻译后修饰。自由基 -腺苷甲硫氨酸（SAM）酶催化许多具有挑战性的化学反应。在 RiPP 生物合成途径中，这些转化包括 C-H、C-C、C-S 和 C-O 键的形成。在本文中，我们表明 基因编码一种自由基 SAM 蛋白，SbtM，它催化最小肽底物中 Cys/SeCys 残基的环化。对这种转化的生化研究支持一种涉及在底物 Cys 的 C-3 上进行 H 原子提取以引发化学变化的机制。考虑了几种可能的环化产物。综合的生化、光谱、质谱和计算观察结果表明硫代恶唑啉是 SbtM 催化修饰的产物。据我们所知，这是第一个催化涉及含 SeCys 肽的转化的自由基 SAM 酶的例子，代表了形成含恶唑啉的 RiPP 天然产物的新范例。
