氨基酸(AA)是模块化和可修改的构建块,自然用于合成两种大分子,如蛋白质,和小分子天然产物,如生物碱和非核糖体肽(NRP)。虽然20种主要的蛋白质AAs显示相对有限的侧链多样性,存在广泛的非规范氨基酸(ncAA),其不被核糖体用于蛋白质合成,但包含在蛋白质AA中未发现的广泛的结构特征和官能团。在这份通讯中,我们报道了一种新的ncAA的生物合成途径的发现,帕扎明,其包含在两个步骤中形成的环丙烷环。第一步,通过自由基卤化酶PazA将氯添加到赖氨酸的C4位。然后在下一步中通过吡哆醛-5'-磷酸依赖性酶形成环丙烷环,PazB,通过对C4的SN2样攻击来消除氯化物。该途径在天然宿主中的遗传研究,假单胞菌,表明帕扎明及其琥珀酰化衍生物,帕扎胺,基于拟南芥幼苗根表型的改变,有可能抑制生长植物中的乙烯生物合成。我们进一步表明PazB可用于制备替代的含环丁烷的AA。这些发现可能会导致特种化学品和农业生物技术的生物催化生产的进步。
Amino acids (AAs) are modular and modifiable building blocks which nature uses to synthesize both macromolecules, such as proteins, and small molecule natural products, such as alkaloids and non-ribosomal peptides (NRPs). While the 20 main proteinogenic AAs display relatively limited side-chain diversity, a wide range of non-canonical amino acids (ncAAs) exist that are not used by the ribosome for protein synthesis but contain a broad array of structural features and functional groups not found in proteinogenic AAs. In this communication, we report the discovery of the biosynthetic pathway for a new ncAA, pazamine, which contains a cyclopropane ring formed in two steps. In the first step, a chlorine is added onto the C4 position of lysine by a radical halogenase PazA. The cyclopropane ring is then formed in the next step by a pyridoxal-5\'-phosphate-dependent enzyme, PazB, via an SN2-like attack onto C4 to eliminate chloride. Genetic studies of this pathway in the native host, Pseudomonas azotoformans, show that pazamine and its succinylated derivative, pazamide, potentially inhibit ethylene biosynthesis in growing plants based on alterations in the root phenotype of Arabidopsis thaliana seedlings. We further show that PazB can be utilized to make an alternative cyclobutane-containing AA. These discoveries may lead to advances in biocatalytic production of specialty chemicals and agricultural biotechnology.