Crystallization and preliminary X-ray analysis of S-ribosylhomocysteinase from Streptococcus mutans

Suppressive effects of gecko cathelicidin on biofilm formation and cariogenic virulence factors of Streptococcus mutans

OBJECTIVE

The aims of this study were to investigate the effectivity of gecko cathelicidin Gj-CATH2 on biofilm formation and cariogenic virulence factors of S. mutans, and preliminary explore its function mechanisms.

DESIGN

Minimum inhibitory concentration and bacterial killing kinetics assays were performed to assess the antimicrobial effect of Gj-CATH2.The influence of Gj-CATH2 on S. mutans biofilm formation was determined by crystal violet staining method and observed by SEM. The effects of Gj-CATH2 on exopolysaccharides (EPS) synthesis, bacterial aggregation, acidogenicity and aciduricity of S. mutans were also investigated. Quantitative real-time PCR was conducted to acquire the expression profile of related genes.

RESULTS

Gj-CATH2 showed strong bactericidal and anti-biofilm effects on S. mutans. SEM confirmed the reduction of the dense structure in S. mutans biofilm in Gj-CATH2-treated groups. Gj-CATH2 significantly inhibited EPS synthesis, cell aggregation, acid production of S. mutans, but showed no influence on its acid proof. Furthermore, the expression of genes related to biofilm formation (gtfB/C/D, gbpB/D), quorum sensing system (luxS and comD/E) and acidogenicity (ldh) was significantly suppressed by Gj-CATH2. Gj-CATH2 also displayed advantageous resistance in human saliva and exhibited negligible toxicity against mammalian cells.

CONCLUSIONS

Gj-CATH2 inhibited S. mutans biofilm formation by targeting the bacterial adhesion and the biofilm maturation stages. Gj-CATH2 significantly suppressed virulence factors production of S. mutans, resulting in decreased EPS synthesis and reduced acidogenicity of bacteria. These findings suggest Gj-CATH2 might be a promising agent for clinical application in prevention of dental caries.

In-Silico Prediction and Modeling of the Quorum Sensing LuxS Protein and Inhibition of AI-2 Biosynthesis in Aeromonas hydrophila

luxS is conserved in several bacterial species, including A. hydrophila, which causes infections in prawn, fish, and shrimp, and is consequently a great risk to the aquaculture industry and public health. luxS plays a critical role in the biosynthesis of the autoinducer-2 (AI-2), which performs wide-ranging functions in bacterial communication, and especially in quorum sensing (QS). The prediction of a 3D structure of the QS-associated LuxS protein is thus essential to better understand and control A. hydrophila pathogenecity. Here, we predicted the structure of A. hydrophila LuxS and characterized it structurally and functionally with in silico methods. The predicted structure of LuxS provides a framework to develop more complete structural and functional insights and will aid the mitigation of A. hydrophila infection, and the development of novel drugs to control infections. In addition to modeling, the suitable inhibitor was identified by high through put screening (HTS) against drug like subset of ZINC database and inhibitor ((-)-Dimethyl 2,3-O-isopropylidene-l-tartrate) molecule was selected based on the best drug score. Molecular docking studies were performed to find out the best binding affinity between LuxS homologous or predicted model of LuxS protein for the ligand selection. Remarkably, this inhibitor molecule establishes agreeable interfaces with amino acid residues LYS 23, VAL 35, ILE76, and SER 90, which are found to play an essential role in inhibition mechanism. These predictions were suggesting that the proposed inhibitor molecule may be considered as drug candidates against AI-2 biosynthesis of A. hydrophila. Therefore, (-)-Dimethyl 2,3-O-isopropylidene-l-tartrate inhibitor molecule was studied to confirm its potency of AI-2 biosynthesis inhibition. The results shows that the inhibitor molecule had a better efficacy in AI-2 inhibition at 40 μM concentration, which was further validated using Western blotting at a protein expression level. The AI-2 bioluminescence assay showed that the decreased amount of AI-2 biosynthesis and downregulation of LuxS protein play an important role in the AI-2 inhibition. Lastly, these experiments were conducted with the supplementation of antibiotics via cocktail therapy of AI-2 inhibitor plus OXY antibiotics, in order to determine the possibility of novel cocktail drug treatments of A. hydrophila infection.

AI-2-mediated signalling in bacteria

Success in nature depends upon an ability to perceive and adapt to the surrounding environment. Bacteria are not an exception; they recognize and constantly adjust to changing situations by sensing environmental and self-produced signals, altering gene expression accordingly. Autoinducer-2 (AI-2) is a signal molecule produced by LuxS, an enzyme found in many bacterial species and thus proposed to enable interspecies communication. Two classes of AI-2 receptors and many layers and interactions involved in downstream signalling have been identified so far. Although AI-2 has been implicated in the regulation of numerous niche-specific behaviours across the bacterial kingdom, interpretation of these results is complicated by the dual role of LuxS in signalling and the activated methyl cycle, a crucial central metabolic pathway. In this article, we present a comprehensive review of the discovery and early characterization of AI-2, current developments in signal detection, transduction and regulation, and the major studies investigating the phenotypes regulated by this molecule. The development of novel tools should help to resolve many of the remaining questions in the field; we highlight how these advances might be exploited in AI-2 quorum quenching, treatment of diseases, and the manipulation of beneficial behaviours caused by polyspecies communities.