Peptide o-aminoanilides as crypto-thioesters for protein chemical synthesis.

Fully unprotected peptide o-aminoanilides can be efficiently activated by NaNO2 in aqueous solution to furnish peptide thioesters for use in native chemical ligation. This finding enables the convergent synthesis of proteins from readily synthesizable peptide o-aminoanilides as a new type of crypto-thioesters. The practicality of this approach is shown by the synthesis of histone H2B from five peptide segments. Purification or solubilization tags, which are sometimes needed to improve the efficiency of protein chemical synthesis, can be incorporated into the o-aminoanilide moiety, as demonstrated in the preparation of the cyclic protein lactocyclicin Q.

Irreversible site-specific hydrazinolysis of proteins by use of sortase.

Sortase-mediated hydrazinolysis of proteins with hydrazine or its derivatives was developed for the production of recombinant protein hydrazides. This process provides an alternative approach for protein semisynthesis through the use of recombinant protein hydrazides as thioester surrogates. It also provides an alternative method for C-terminal modification of proteins with functional units as well as for the preparation of C-to-C fusion proteins.

Stable, polyvalent aptamer-conjugated near-infrared fluorescent nanocomposite for high-performance cancer cell-targeted imaging and therapy.

Early diagnosis and targeted therapy are two important ways to improve cancer treatment survival. In this work, via a simple DNA hybridization reaction, DNA-templated fluorescent silver nanoclusters (AgNCs) were successfully assembled around a DNA-modified gold nanoparticle (AuNP) to construct a novel nanocomposite with the functions of cancer cell-specific imaging and targeted therapy. The as-prepared AuNP@(AS1411-AgNCs)n nanocomposite shows strong near-infrared fluorescence emission and improved biostability, and carries a high density of AS1411-the first anticancer aptamer targeting nucleolin protein, which is over-expressed not only on the surface but also in the cytoplasm of cancer cells. The synergy of multivalent AS1411-nucleolin binding promotes accumulation of the nanocomposite towards cancer cells and subsequent internalization in them. This results in highly specific cancer cell-targeted imaging and selective killing in a low AuNP@(AS1411-AgNCs)n concentration range. The prepared nanocomposite also shows great potential as a carrier of doxorubicin to further promote the selective killing of cancer cells.

G-quadruplex fluorescent probe-mediated real-time rolling circle amplification strategy for highly sensitive microRNA detection.

Real-time PCR has revolutionized PCR from qualitative to quantitative. As an isothermal DNA amplification technique, rolling circular amplification (RCA) has been demonstrated to be a versatile tool in many fields. Development of a simple, highly sensitive, and specific strategy for real-time monitoring of RCA will increase its usefulness in many fields. The strategy reported here utilized the specific fluorescence response of thioflavin T (ThT) to G-quadruplexes formed by RCA products. Such a real-time monitoring strategy works well in both traditional RCA with linear amplification efficiency and modified RCA proceeded in an exponential manner, and can be readily performed in commercially available real-time PCR instruments, thereby achieving high-throughput detection and making the proposed technique more suitable for biosensing applications. As examples, real-time RCA-based sensing platforms were designed and successfully used for quantitation of microRNA over broad linear ranges (8 orders of magnitude) with a detection limit of 4 aM (or 0.12 zmol). The feasibility of microRNA analysis in human lung cancer cells was also demonstrated. This work provides a new method for real-time monitoring of RCA by using unique nucleic acid secondary structures and their specific fluorescent probes. It has the potential to be extended to other isothermal single-stranded DNA amplification techniques.

Facile synthesis of CdTe@GdS fluorescent-magnetic nanoparticles for tumor-targeted dual-modal imaging.

Multimodal imaging has made great contribution for diagnosis and therapy of disease since it can provide more effective and complementary information in comparison to any single imaging modality. The design and fabrication of fluorescent-magnetic nanoparticles for multimodal imaging has rapidly developed over the years. Herein, we demonstrate the facile synthesis of GdS coated CdTe nanoparticles (CdTe@GdS NPs) as multimodal agents for fluorescence (FL) and T1-weighted magnetic resonance (MR) imaging. These nanoparticles obtain both prominent fluorescent and paramagnetic properties by coating the GdS shell on the surface of CdTe core via a simple room-temperature route in aqueous solution directly. It is shown that the as-prepared CdTe@GdS NPs have high quantum yield (QY) value of 12% and outstanding longitudinal relaxation rate (r1) of 11.25 mM s(-1), which allow them to be employed as FL/MR dual-modal imaging contrast agents. They also exhibit small particle size of 5 nm, excellent colloidal stability and low cellular toxicity for concentrations up to 750 µg mL(-1). In addition, with the conjugation of folic acid, the nanoparticles were successfully used for tumor-targeted FL/MR dual-modal imaging in vitro and in vivo.