Abstract：
Elaiophylin (Ela), a unique 16-membered symmetric macrodiolide antibiotic, displays broad biological activity. Two rare 2-deoxy-L-fucose moieties at the ends of Ela are critical for its activity. Previously, elaiophylin glycosyltransferase (ElaGT) was identified as the enzyme that is responsible for the symmetric glycosylation of Ela, acting as a potential enzymatic tool for enhancing the diversity and activity of Ela. However, a symmetric catalytic mechanism has never been reported for a glycosyltransferase (GT). To explore the catalytic mechanism, the structure of ElaGT was determined in four forms: the apo form and Ela-bound, thymidine diphosphate-bound and uridine diphosphate-bound forms. In the Ela-bound structure, two ElaGTs form a `face-to-face\' C2-symmetric homodimer with a continuous acceptor-binding pocket, allowing a molecule of Ela to shuffle through. Interestingly, this dimer interface resembles that of the activator-dependent GT EryCIII with its activator EryCII. Sequence analysis also indicates that ElaGT belongs to the activator-dependent GT family, but no putative activator has been identified in the Ela gene cluster. It was then found that the ElaGT homodimer may utilize this `face-to-face\' arrangement to stabilize the Ela-binding loops on the interface and to simultaneously allosterically regulate the catalytic center. Therefore, these structures present a novel self-activating model for symmetric sugar transfer in the GT family and a new potential regulation site for substrate specificity.
摘要：
Elaiophlin（Ela），一种独特的16元对称大二内酯抗生素，具有广泛的生物活性。Ela末端的两个罕见的2-脱氧-L-岩藻糖部分对其活性至关重要。以前,elaiphylin糖基转移酶（ElaGT）被鉴定为负责Ela的对称糖基化的酶，作为增强Ela多样性和活性的潜在酶促工具。然而,糖基转移酶（GT）的对称催化机理从未被报道。探索催化机理,ElaGT的结构以四种形式确定：apo形式和Ela结合，胸苷二磷酸结合和尿苷二磷酸结合形式。在Ela绑定结构中，两个ElaGT形成一个“面对面”的C2对称同二聚体，带有一个连续的受体结合口袋，让一个伊拉分子洗牌通过。有趣的是,该二聚体界面类似于激活剂依赖性GTEryCIII及其激活剂EryCII的界面。序列分析还表明ElaGT属于激活剂依赖性GT家族，但是在Ela基因簇中没有发现推定的激活剂。然后发现ElaGT同二聚体可以利用这种“面对面”排列来稳定界面上的Ela结合环，并同时变构调节催化中心。因此,这些结构为GT家族中的对称糖转移提供了新的自激活模型，并为底物特异性提供了新的潜在调节位点。
