No abstract

N-Acyl homoserine lactone (AHL) quorum-sensing signals are the vital elements of bacterial quorum-sensing systems, which regulate diverse biological functions, including virulence. The AHL-lactonase, a quorumquenching enzyme encoded by aiiA from Bacillus sp., inactivates AHLs by hydrolyzing the lactone bond to produce corresponding N-acyl homoserines. To characterize the enzyme, the recombinant AHL-lactonase and its four variants were purified. Kinetic and substrate specificity analysis showed that AHL-lactonase had no or little residue activity to non-acyl lactones and noncyclic esters, but displayed strong enzyme activity toward all tested AHLs, varying in length and nature of the substitution at the C3 position of the acyl chain. The data also indicate that the amide group and the ketone at the C1 position of the acyl chain of AHLs could be important structural features in enzyme-substrate interaction. Surprisingly, although carrying a 104 HX-HXDH 109 short sequence identical to the zinc-binding motif of several groups of metallohydrolytic enzymes, AHL-lactonase does not contain or require zinc or other metal ions for enzyme activity. Except for the amino acid residue His-104, which was shown previously to not be required for catalysis, kinetic study and conformational analysis using circular dichroism spectrometry showed that substitution of the other key residues in the motif (His-106, Asp-108, and His-109), as well as His-169 with serine, respectively, caused conformational changes and significant loss of enzyme activity. We conclude that AHL-lactonase is a highly specific enzyme and that the 106 HXDH 109 ϳH 169 of AHL-lactonase represents a novel catalytic motif, which does not rely on zinc or other metal ions for activity.Many host-associated bacteria produce, release, and respond to small signal molecules to monitor their own population density and control the expression of specific genes in response to change in population density. This type of gene regulation, which controls diverse biological functions including virulence and biofilm formation, is known as quorum-sensing (QS) 1 (1-4). In general, each individual bacterial cell produces a basal level of QS signals. The signals accumulate to a threshold concentration as the cells proliferate and interact with their cognate transcription factors to activate gene expression. Several groups of QS signals have been identified. Among them, N-acyl homoserine lactones (AHLs) comprise a family of QS signals identified in many Gram-negative bacteria, in particular, Proteobacteria. Different bacterial species may produce different AHLs, which vary in the length and substitution of the acyl chain but maintain the same homoserine lactone moiety (1, 3, 4). These structural variations could constitute the basis of signaling specificity of AHL molecules (5, 6).The AHL-dependent QS system has drawn considerable attention over the last 10 years, as it is involved in the regulation of diverse and important biological functions, in particular, the virulence gene expressi...

A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).

Sensitive and selective detection for cancer biomarkers are critical in cancer clinical diagnostics. Here we developed a microfluidic protein chip for an ultrasensitive and multiplexed assay of cancer biomarkers. Aqueous-phase-synthesized CdTe/CdS quantum dots (aqQDs) were employed as fluorescent signal amplifiers to improve the detection sensitivity. Secondary antibodies (goat anti-mouse IgG) were conjugated to luminescent CdTe/CdS QDs to realize a versatile fluorescent probe that could be used for multiplexed detection in both sandwich and reverse phase immunoassays. We found that our microfluidic protein chip not only possessed ultrahigh femtomolar sensitivity for cancer biomarkers, but was selective enough to be directly used in serum. This protein chip thus combines the high-throughput capabilities of a microfluidic network with the high sensitivity and multicolor imaging ability offered by highly fluorescent QDs, which can become a promising diagnostic tool in clinical applications.

Antibacterial agents with high antibacterial efficiency and bacteria-binding capability are highly desirable. Herein, we describe the successful preparation of Cu2WS4 nanocrystals (CWS NCs) with excellent antibacterial activity. CWS NCs with small size (∼20 nm) achieve more than 5 log (>99.999%) inactivation efficiency of both Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) at low concentration (<2 μg mL–1) with or without ambient light, which is much better than most of the reported antibacterial nanomaterials (including Ag, TiO2, etc.) and even better than the widely used antibiotics (vancomycin and daptomycin). Antibacterial mechanism study showed that CWS NCs have both enzyme-like (oxidase and peroxidase) properties and selective bacteria-binding ability, which greatly facilitate the production of reactive oxygen species to kill bacteria. Animal experiments further indicated that CWS NCs can effectively treat wounds infected with methicillin-resistant Staphylococcus aureus (MRSA). This work demonstrates that CWS NCs have the potential as effective antibacterial nanozymes for the treatment of bacterial infection.