Mechanism and scope of azetidine-1-carboxylic acid synthases

氮杂丁-1-羧酸（AZE）是一种非规范的氨基酸，被发现是几种微生物次生代谢产物的组成部分，具有有趣的性质。最近的研究表明，AZE是通过AZE合成酶的作用由s-腺苷基蛋氨酸（SAM）衍生而来，AZE合成酶类似于i类甲基转移酶，因此在序列数据库中经常被错误注释。本文提出的研究旨在揭示AZE合成酶的催化机制，利用Saccharotrix sp. NRRL B-16348中未发表的酶的晶体结构，以及来自FOR其他基团的SAM衍生物，作为基于结构的生化方法的跳板。此外，通过利用在FOR中可用的非天然SAM衍生物的收集，AZE合成酶的底物光谱将被分析，可能导致新的同源物并入含有AZE的天然产物。最后，将研究先前未被鉴定的与AZE合酶序列相似性显著的蛋白质，以确定AZE合酶的一般序列特征，并潜在地发现催化新型sam依赖反应的酶。

Azetidine-1-carboxylic acid (AZE) is a non-canonical ⍺-amino acid found as a building block of several microbial secondary metabolites with interesting properties. It has recently been shown that AZE is derived from S-adenosyl-methionine (SAM) via the action of AZE synthases, enzymes that resemble class-I methyltransferases and that are hence commonly misannotated in sequence databases. The research proposed here aims at unravelling the catalytic mechanism of AZE synthases, using the unpublished crystal structure of an enzyme from Saccharotrix sp. NRRL B-16348 together with SAM derivatives sourced from other groups of the FOR as a springboard for a structure-based biochemical approach. Further, by tapping into the collection of non-natural SAM derivatives that will become available within the FOR, the substrate spectrum of AZE synthases will be analyzed, potentially leading to new congeners for incorporation into AZE-containing natural products. Finally, previously uncharacterized proteins with significant sequence similarity to AZE synthase will be investigated to identify general sequence signatures of AZE synthases and to potentially discover enzymes that catalyze novel SAM-dependent reactions.