Studies On Antibacterial Quantitative Structure-activity Relationship Against Escherichia Coli Of Flavoniods Based On The Inhibition Of DNA Gyrase

Flavonoids are a family of plant-derived compounds with potentially exploitable activities, including direct antibacterial activity, synergism with antibiotics, and suppression of bacterial virulence, which could be good natural preservative. In this study, we choose Escherichia coli DNA gyrase as the inhibitory role of flavonoids’ target and figure out the relationship between their structure and inhibition of DNA gyrase. In addtion, we present the CoMFA analysis and CoMSIA analysis (3D-QSAR) of the antimicrobial activity of 30 flavonoids compounds against Escherichia coli. The main research subjects and results are listed as follows: 1. Specific primers were designed, and gyrA and gyrB genes of Escherichia coli DH5a strain were amplified by PCR, respectively. And then cloning plasmids and expression plasmids were constructed. SDS-PAGE was used to analyze the results of protein expression that gyrA protein 96.9KDa (purity>95%) and gyrB protein 89.9Kda(purity>95%).2. The study was performed to evaluate activity of the recombinant protein gyrA and gyrB gyrase and inhibitory effects of 10 flavonoids on DNA gyrase. The comparative analysis about inhibition on DNA gyrase and structure of 10 flavonoids was in order to elucidate the structure-activity relationships of flavonoids. The structure-activity relationship analysis revealed that for good inhibitory effect, the 5-OH,7-OH and 8-OCH3 functionalities were essential, while the presence of 3-OH and 3’-OCH3 greatly reduced inhibition.3. The inhibitory effects of 30 flavonoids on Escherichia coli were evaluated by using microbroth dilution assay, represented by EC50. The range of most flavonoids were 500-50μg/mL. Based on this, we get the structure-activity relationship analysis revealed that for good inhibitory effect as following:Glycosidic group on C-7 and C-8,3’-OCH3 and 3’-OH could reduce inhibition, while 8-OCH3 and 4’-OH could enhance inhibition of flavonoids.4. This study was performed to establish 3D-QSAR models able to predict flavonoids with high anti-Escherichia coli activity and understand their structure-activity relationships. The model has been established by using a training set of 25 flavonoids with cross-validated q2=0.538/0.598, non-cross-validated r2=0.987/0.986 for the best CoMFA/CoMSIA models. Additionally, the contour map results suggested that structural characteristics of flavonoids favorable for the high anti-Escherichia coli activity might include:bulky substituent groups on A ring C-5, C-6, C-7, B ring C-3’and C ring C-3; electron-donating groups on A ring C-5, C-6, C-7, B ring C-4’; hydrogen-bond donor groups on the A ring C-7 and C ring C-3; hydrophobic groups on A ring C-8 and C ring C-3.