Bacteria produce and respond to signal molecules depending on their cell density. This process is called “quorum sensing”. The ComX pheromone, controlled by quorum sensing, activates natural genetic competence in Bacillus subtilis. ComX is an oligopeptide with a posttranslational modification. It has been suggested that ComX pheromone is modified with an isoprenoid at its tryptophan residue, but the complete chemical structure is unknown. We first determined the molecular formula of ComXRO-E-2, a competence factor for B. subtilis strain RO-E-2. Then we synthesized putative pheromones with 1-, 2-, 4-, 5-, 6-, or 7-geranyl substituted tryptophan residues. The regio- and stereo-selective synthesis of the geranyl tryptophans was successful, and we prepared the six peptides with modified tryptophan residues. These peptides had the same molecular formula and showed similar hydrophobicity to the natural ComXRO-E-2 in LC–MS analysis. But, none of them showed the same retention time as the natural pheromone and none exhibited its biological activity. These results suggest that the isoprenoid modification pattern of the tryptophan residue is more complex than postulated.
细菌会根据其细胞密度产生信号分子并做出反应。这一过程被称为 "法定人数感应"。由法定人数感应控制的 ComX 信息素能激活
枯草芽孢杆菌的自然遗传能力。ComX 是一种带有翻译后修饰的寡肽。有研究认为,ComX信息素在其色
氨酸残基处被异
戊烯类化合物修饰,但其完整的
化学结构尚不清楚。我们首先确定了枯草杆菌菌株 RO-E-2 的能力因子 ComXRO-E-2 的分子式。然后,我们合成了具有 1、2、4、5、6 或 7 个芳基取代色
氨酸残基的推定信息素。我们成功地进行了香叶基色
氨酸的区域和立体选择性合成,并制备了六种具有修饰色
氨酸残基的肽。这些肽具有相同的分子式,在 LC-MS 分析中显示出与天然 ComXRO-E-2 相似的疏
水性。但是,它们都没有表现出与天然信息素相同的保留时间,也没有表现出其
生物活性。这些结果表明,色
氨酸残基的
异戊二烯修饰模式比推测的更为复杂。