6-Tuliposides A (PosA) and B (PosB) are glucose esters accumulated in tulip (Tulipa gesneriana) as major defensive secondary metabolites. Pos-converting enzymes (TgTCEs), which we discovered previously from tulip, catalyze the conversion reactions of PosA and PosB to antimicrobial tulipalins A (PaA) and B (PaB), respectively. The TgTCEs, belonging to the carboxylesterase family, specifically catalyze intramolecular transesterification, but not hydrolysis. In this report, we synthesized analogues of Pos with various alcohol moieties, and measured the TgTCE activity together with a determination of the kinetic parameters for these analogues with a view to probe the substrate recognition mechanism of the unique non-ester-hydrolyzing TgTCEs. It was found that d-glucose-like structure and number of the hydroxyl group in alcohol moiety are important for substrate recognition by TgTCEs. Among the analogues examined, 1,2-dideoxy analogues of PosA and PosB were found to be recognized by the TgTCEs more specifically than the authentic substrates by lowering Km values. The present results will provide a basis for designing simple, stable synthetic substrate analogues for crystallographic analysis of TgTCEs.

中文翻译：

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郁金香脂质体转化酶的底物特异性，郁金香中独特的非酯水解性羧酸酯酶：底物醇部分对酶活性的影响。

6-Tuliposides A（PosA）和B（PosB）是作为主要防御性次要代谢产物积聚在郁金香（Tulipa gesneriana）中的葡萄糖酯。我们先前从郁金香中发现的Pos转换酶（TgTCEs）分别催化PosA和PosB分别转化为抗菌性郁金香脂蛋白A（PaA）和B（PaB）的反应。属于羧酸酯酶家族的TgTCEs特异性催化分子内酯交换反应，但不催化水解。在本报告中，我们合成了具有各种醇基的Pos类似物，并测量了TgTCE活性，并确定了这些类似物的动力学参数，以期探索独特的非酯水解TgTCEs的底物识别机制。已经发现，d-葡萄糖样结构和醇部分中羟基的数目对于TgTCE识别底物很重要。在检测的类似物中，发现通过降低Km值，TgTCE比真实的底物更能特异性地识别PosA和PosB的1,2-二脱氧类似物。本结果将为设计用于TgTCE晶体学分析的简单，稳定的合成底物类似物提供基础。