Correction: Monitoring metal-amyloid-ß complexation by a FRET-based probe: design, detection, and inhibitor screening.

[This corrects the article DOI: 10.1039/C8SC04943B.].

Monitoring metal-amyloid-ß complexation by a FRET-based probe: design, detection, and inhibitor screening.

Aggregation of amyloidogenic peptides could cause the onset and progression of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. These amyloidogenic peptides can coordinate to metal ions, including Zn(ii), which can subsequently affect the peptides' aggregation and toxicity, leading to neurodegeneration. Unfortunately, the detection of metal-amyloidogenic peptide complexation has been very challenging. Herein, we report the development and utilization of a probe (A-1) capable of monitoring metal-amyloid-ß (Aß) complexation based on Förster resonance energy transfer (FRET). Our probe, A-1, is composed of Aß1-21 grafted with a pair of FRET donor and acceptor capable of providing a FRET signal upon Zn(ii) binding even at nanomolar concentrations. The FRET intensity of A-1 increases upon Zn(ii) binding and decreases when Zn(ii)-bound A-1 aggregates. Moreover, as the FRET intensity of Zn(ii)-added A-1 is drastically changed when their interaction is disrupted, A-1 can be used for screening a chemical library to determine effective inhibitors against metal-Aß interaction. Eight natural products (out of 145 compounds; >80% inhibition) were identified as such inhibitors in vitro, and six of them could reduce Zn(ii)-Aß-induced toxicity in living cells, suggesting structural moieties useful for inhibitor design. Overall, we demonstrate the design of a FRET-based probe for investigating metal-amyloidogenic peptide complexation as well as the feasibility of screening inhibitors against metal-bound amyloidogenic peptides, providing effective and efficient methods for understanding their pathology and finding therapeutic candidates against neurodegenerative disorders.

Label-Free Detection of Protein Tyrosine Phosphatase 1B (PTP1B) by Using a Rationally Designed Förster Resonance Energy Transfer (FRET) Probe.

A highly selective detection method of native protein tyrosine phosphatase 1B (PTP1B) is described using a target specific probe equipped with 1-naphthylamine (λex =330 nm, λem =445 nm). Irradiation of a mixture of PTP1B and Probe 1 with ultraviolet light of 280 nm (corresponding to PTP1B excitation maximum) resulted in significant fluorescence increase at 445 nm, following FRET characteristics. This phenomenon does not occur with other closely related phosphatases or cellular abundant alkaline phosphatase (APP). Probe 1, the most potent and selective probe, was found to competitively inhibit PTP1B (Ki ≈42 nm), whereas APP inhibition was found to be in the low micromolar range. Furthermore, Probe 1 discriminates between PTP1B and several other phosphatases. Here, we report real-time label-free FRET detection of pure PTP1B as well as induced human PTP1B in Escherichia coli cell lysate. In contrast to 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP), a representative fluorescence turn-on PTP substrate, our FRET probe successfully differentiated human cervical carcinoma cell lysate, SiHa, which has a high expression level of PTP1B, from PTP1B-knockdown SiHa cell lysate (that is, siRNA was used for PTP1B knockdown).

Functionalized protein nanocages as a platform of targeted therapy and immunodetection.

To improve the therapeutic/diagnostic potentials of drugs and/or imaging contrast agents, various targeted delivery systems are actively being developed. Especially protein nanocages, hollow and highly symmetrical nanometer-sized cage structures that are self-assembled from multiple protein subunits, are emerging as powerful targeted delivery tools. Their natural abundance, biocompatibility, low toxicity, well defined size and high symmetry are a few of the favorable characteristics which render protein nanocages as near ideal carriers for pharmaceuticals and/or imaging probes. This review aims to highlight current progress in the development and application of protein nanocages in targeted drug delivery approaches with an emphasis on the use of antibodies as targeting motifs to achieve high selectivity toward specific targets.

Synthesis and Evaluation of Hybrid Structures Composed of Two Glucosylceramide Synthase Inhibitors.

Glucosylceramide metabolism and the enzymes involved have attracted significant interest in medicinal chemistry, because aberrations in the levels of glycolipids that are derived from glucosylceramide are causative in a range of human diseases including lysosomal storage disorders, type 2 diabetes, and neurodegenerative diseases. Selective modulation of one of the glycoprocessing enzymes involved in glucosylceramide metabolism-glucosylceramide synthase (GCS), acid glucosylceramidase (GBA1), or neutral glucosylceramidase (GBA2)-is therefore an attractive research objective. In this study we took two established GCS inhibitors, one based on deoxynojirimycin and the other a ceramide analogue, and merged characteristic features to obtain hybrid compounds. The resulting 39-compound library does not contain new GCS inhibitors; however, a potent (200 nm) GBA1 inhibitor was identified that has little activity toward GBA2 and might therefore serve as a lead for further biomedical development as a selective GBA1 modulator.

Intrinsic tryptophan fluorescence in the detection and analysis of proteins: a focus on Förster resonance energy transfer techniques.

Förster resonance energy transfer (FRET) occurs when the distance between a donor fluorophore and an acceptor is within 10 nm, and its application often necessitates fluorescent labeling of biological targets. However, covalent modification of biomolecules can inadvertently give rise to conformational and/or functional changes. This review describes the application of intrinsic protein fluorescence, predominantly derived from tryptophan (λ EX ≈ 280 nm, λ EM ≈ 350 nm), in protein-related research and mainly focuses on label-free FRET techniques. In terms of wavelength and intensity, tryptophan fluorescence is strongly influenced by its (or the proteinlocal environment, which, in addition to fluorescence quenching, has been applied to study protein conformational changes. Intrinsic Förster resonance energy transfer (iFRET), a recently developed technique, utilizes the intrinsic fluorescence of tryptophan in conjunction with target-specific fluorescent probes as FRET donors and acceptors, respectively, for real time detection of native proteins.