克雷白氏菌為一伺機型病原菌，常見於台灣的院內感染，造成嚴重的疾病，且目前已具有多重抗生素抗藥性，臨床治療不易。由於任何生物的DNA複製為一必須程序，其中DnaB解旋酶負責解開雙股DNA為單股DNA，此功能是極其重要的，可能可做為重要的標靶。本研究利用天然植物中含有的多酚類物質—黃酮醇：galangin、kaempferol、quercetin、myricetin，去觀察其對於DnaB與dNTP、單股DNA結合、與解旋活性的影響。我們初步發現DnaB與myricetin的結合能力最強，並抑制了DnaB與dNTP結合，與單股DNA之結合能力及其雙股DNA解旋能力；但抑制DnaB與dNTP結合能力最強的則是galangin。根據模擬蛋白質與小分子的結構，並預測其結合狀況，結果顯示黃酮醇分子是結合在nucleotide結合位上，導致其後續的活性，單股DNA結合之能力與解旋活性下降。經由其結合相關之胺基酸序列分析，我們發現這些胺基酸在不同菌種中皆為高度保留，故此抑制作用機制除了在克雷白氏菌外，應可見於其他菌種中。此研究初步驗證了黃酮醇分子，尤其是myricetin 與galangin，可以抑制DnaB解旋酶的活性，且極可能來自於抑制其dNTP的結合能力，因此黃酮醇可望作為抑制此DnaB活性的前導藥物。
Klebsiella pneumoniae is a ubiquitous opportunistic pathogen, and many clinical strains are highly resistant to antibiotics in Taiwan. DNA replication is a basic process required for life, where DnaB helicase plays an important role in unwinding dsDNA and can be a prime target in antibiotic development. In this study, we found that several flavonol compounds, galangin, kaempferol, quercetin, and myricetin, can interact with DnaB helicase. We further showed that the dNTP and ssDNA binding, as well as the dsDNA unwinding activity of DnaB helicase can be inhibited by these flavonols. Although myricetin binds to DnaB helicase with highest affinity among the flavonols and displays its inhibition of ssDNA-DnaB binding and the unwinding activity, it does not show the highest inhibition of dNTP-DnaB binding; galangin displays the highest inhibition of dNTP-DnaB binding. According to the modeling structures, the flavonol binds to the nucleotide binding site of DnaB, thereby causes varying degree of inhibition. The flavonol-interacting residues of DnaB are highly conserved among bacterial strains. These results suggest that flavonols, especially myricetin and galangin, seems likely to be as leads for drug development in inhibiting the DnaB activity.
