A novel dextran-grafted tetrapeptide resin for antibody purification.

Short peptide biomimetic affinity chromatography as a novel antibody separation chromatography is a potential alternative to protein A chromatography. However, if directly attaching ligand to matrix, the adsorption capacity and mass transfer rate would be affected by pore blockage and steric effect. Grafting resin is an effective method to solve this problem by using polymer as a bridge between matrix and ligand. In this work, a novel resin was prepared by grafting a tetrapeptide to the dextran-grafted matrix. Then, the adsorption properties for human immunoglobin G and BSA were determined. The results showed the saturation adsorption capacity could reach to 133 mg/g resin at pH 8.9 with a significantly low dissociation constant (0.03 mg/mL). The influence of flow rates to dynamic binding capacity of this resin was less than that of the non-grafted resin. The separation performance of the resin showed monoclonal antibody could be well isolated from the Chinese hamster ovary culture supernatant at pH 9.0 with the purity of 93.0% and yield of 84.7% by one step. Overall, this resin could achieve higher binding capacity by the possible of gaining higher ligand density, indicating its potential significance for separation in larger scale systems.

Dual-signal-amplified electrochemiluminescence biosensor for microRNA detection by coupling cyclic enzyme with CdTe QDs aggregate as luminophor.

In this work, a dual-signal-amplified electrochemiluminescence (ECL) biosensor was proposed for the first time to detect microRNAs (miRNAs) based on cyclic enzyme and seeded-watermelon-like mesoporous nanospheres (mSiO2@CdTe@SiO2, mSQS NSs). mSQS NSs were successfully fabricated by inlaying the CdTe quantum dots (QDs) into the mesoporous silica (mSiO2) and future coating the surface with the silica layer. The obtained mSQS NSs contained tens of QDs and exhibited much stronger ECL signal than single QDs. The ECL biosensor achieved firstly signal amplification by using mSQS NSs to label the functional oligonucleotide probe (DNA-F) as enhanced ECL signal probes. Well-dispersed Fe3O4@Au nanoparticles were prepared as immobilization matrices to load hairpin-structured DNA probe (DNA-P). When the target miRNAs were present, hairpin DNA undertook conformation changes. Meanwhile, RNA/DNA duplexes was formed which cleaved by duplex-specific nuclease (DSN) to release miRNAs. Target miRNAs were cycled to hybridize with hairpin DNA, which achieved secondly signal amplification of the ECL biosensor. Thereafter, the complementarily parts between DNA-F and the rest DNA-P generated conjugates. The obtained conjugates would be collected on the surface of the electrode by effecting of magnet. Under the optimal conditions, the developed biosensor showed a wide linear range from 0.1 pM to 100 pM with a low detection limit of 33 fM (S/N = 3). The results of detection for the stability, specificity and reproducibility of ECL biosensor were outstanding. Simultaneously, the potential application of ECL biosensor was verified by using biosensor in serum sample.

SPC-P1: a pathogenicity-associated prophage of Salmonella paratyphi C.

BACKGROUND: Salmonella paratyphi C is one of the few human-adapted pathogens along with S. typhi, S. paratyphi A and S. paratyphi B that cause typhoid, but it is not clear whether these bacteria cause the disease by the same or different pathogenic mechanisms. Notably, these typhoid agents have distinct sets of large genomic insertions, which may encode different pathogenicity factors. Previously we identified a novel prophage, SPC-P1, in S. paratyphi C RKS4594 and wondered whether it might be involved in pathogenicity of the bacteria. RESULTS: We analyzed the sequence of SPC-P1 and found that it is an inducible phage with an overall G+C content of 47.24%, similar to that of most Salmonella phages such as P22 and ST64T but significantly lower than the 52.16% average of the RKS4594 chromosome. Electron microscopy showed short-tailed phage particles very similar to the lambdoid phage CUS-3. To evaluate its roles in pathogenicity, we lysogenized S. paratyphi C strain CN13/87, which did not have this prophage, and infected mice with the lysogenized CN13/87. Compared to the phage-free wild type CN13/87, the lysogenized CN13/87 exhibited significantly increased virulence and caused multi-organ damages in mice at considerably lower infection doses. CONCLUSIONS: SPC-P1 contributes pathogenicity to S. paratyphi C in animal infection models, so it is possible that this prophage is involved in typhoid pathogenesis in humans. Genetic and functional analyses of SPC-P1 may facilitate the study of pathogenic evolution of the extant typhoid agents, providing particular help in elucidating the pathogenic determinants of the typhoid agents.