Development of a peptide-based affinity matrix and detection reagent is important for biomedical research and the biopharmaceutical industry. In the present work, we designed and synthesized an immunoglobin G (IgG)-binding peptide ligand, Fc-III-4C. Fc-III-4C is composed of 15 residues, and the 4 cysteine residues form 2 disulfide bonds to generate a double cyclic structure. The binding affinity of the Fc-III-4C peptide toward human IgG was determined to be 2.45 nM (Kd), which is higher than that of IgG with Protein A/G (Pro-A/G). Importantly, the Fc-III-4C peptide displayed high affinity to various IgGs from different species. Fc-III-4C immobilized agarose beads exhibited high stability and reusability when compared with that of the Pro-A/G-immobilized beads. The conjugate of Fc-III-4C with FITC was demonstrated to be suitable for immunofluorescence detection of proteins expressed in cells. These results demonstrate that the Fc-III-4C peptide is a useful affinity ligand for antibody purification and as a protein detection reagent.

•Establish local endogenous metabolite databases economically.•Build workflow of orbitrap based high throughput untargeted metabolomics analysis.•Efficiently analyze large batches of data from DDA mode.•Enable fast and confident metabolite identification with MS/MS confirmation.•Identification of hundreds of metabolites or lipids from single experiment.Our method aims to establish local endogenous metabolite databases economically without purchasing chemical standards, giving strong bases for following orbitrap based high throughput untargeted metabolomics analysis. A new approach here is introduced to construct metabolite databases on the base of biological sample analysis and mathematic extrapolation. Building local metabolite databases traditionally requires expensive chemical standards, which is barely affordable for most research labs. As a result, most labs working on metabolomics analysis have to refer public libraries, which is time consuming and limited for high throughput analysis. Using this strategy, a high throughput orbitrap based metabolomics platform can be established at almost no cost within a couple of months. It enables to facilitate the application of high throughput metabolomics analysis to identify disease-related biomarkers or investigate biological functions using orbitrap.

We report a unified strategy for the total syntheses of (−)-psychotriasine and (+)-pestalazine B based on the advanced intermediates of 3α-amino-hexahydropyrrolo[2,3-b]indole. To construct these structural motifs, a cascade reaction involving a BINOL-derived phosphoric anion-paired catalyst for enantioselective or diastereoselective azo-coupling/iminium-cyclizations was developed. The remaining key steps of the synthesis involve a sterically hindered amination via hypervalent iodine reagents and the Larock annulation. These transformations enable a general approach to the syntheses of indole alkaloids containing a 3α-amino-hexahydropyrrolo[2,3-b]indole motif and could be further applied to build a natural product-based library.

•A method based on click reaction was designed to enrich glutathionylated peptides•The glutathionylomes of E. coli and Drosophila were profiled•The glutathionylation of metabolic enzymes is conserved among species•Cysteines next to negatively charged amino acids are prone to glutathionylationProtein glutathionylation is an important post-translational modification that regulates many cellular processes, including energy metabolism, signal transduction, and protein homeostasis. Global profiling of glutathionylated proteins (denoted as glutathionylome) is crucial for understanding redox-regulated signal transduction. Here, we developed a novel method based on click reaction and proteomics to enrich and identify the glutathionylated peptides in Escherichia coli and Drosophila lysates, in which 937 and 1,930 potential glutathionylated peptides were identified, respectively. Bioinformatics analysis showed that the cysteine residue next to negatively charged amino acid residues has a higher frequency of glutathionylation. Importantly, we found that most proteins associated with metabolic pathways were glutathionylated and that the glutathionylation sites of metabolic enzymes were highly conserved among different species. Our results indicate that the glutathione analog is a useful tool to characterize protein glutathionylation, and glutathionylation of metabolic enzymes, which play important roles in regulating cellular metabolism, is conserved.Figure optionsDownload full-size imageDownload high-quality image (135 K)Download as PowerPoint slide

Glutathione (GSH) is the most abundant tripeptide in human cells and plays an important role in protecting cells’ integrity against oxidative stress. GSH has an unusual amide linkage formed between the γ-carboxylic group of the glutamic acid in its side-chain and the amine group of cysteine residue. In the present study, we have compared reactivities of GSH to its isomer GluCysGly (ECG), which has a regular amide bond formed between the α-carboxylic group of glutamic acid and the amine group of cysteine residue. The fragmentation pattern of GSH ions in the gas phase is different from that of ECG ions, showing that the loss of H2O is the major dissociation pathway in ECG fragmentation. This is consistent with the dissociation pathway predicted by density functional calculation. Formation of GSSG from oxidation of GSH is faster than that of ECG disulfide, and the gas phase fragmentation pattern of GSSG is different from that of ECG disulfide. GSH and ECG display similar rates in nucleophilic aromatic substitution when reacting with 1-chloro-2,4-dinitrobenzene (CDNB). However, in the presence of glutathione S-transferases (GST), substitution of CDNB by GSH is 10 times faster than that by ECG. GSH and ECG also show differences in clustering patterns in the gas phase. Taken together, our results shed light on understanding effects of unique boding structure in GSH on its stability and reactivities.

In the present study, we have established a new methodology to analyze saliva proteins from HIV-1-seropositive patients before highly active antiretroviral therapy (HAART) and seronegative controls. A total of 593 and 601 proteins were identified in the pooled saliva samples from 5 HIV-1 subjects and 5 controls, respectively. Forty-one proteins were found to be differentially expressed. Bioinformatic analysis of differentially expressed salivary proteins showed an increase of antimicrobial proteins and decrease of protease inhibitors upon HIV-1 infection. To validate some of these differentially expressed proteins, a high-throughput quantitation method was established to determine concentrations of 10 salivary proteins in 40 individual saliva samples from 20 seropositive patients before HAART and 20 seronegative subjects. This method was based on limited protein separation within the zone of the stacking gel of the 1D SDS PAGE and using isotope-coded synthetic peptides as internal standards. The results demonstrated that a combination of protein profiling and targeted quantitation is an efficient method to identify and validate differentially expressed salivary proteins. Expression levels of members of the calcium-binding S100 protein family and deleted in malignant brain tumors 1 protein (DMBT1) were up-regulated while that of Mucin 5B was down-regulated in HIV-1 seropositive saliva samples, which may provide new perspectives for monitoring HIV-infection and understanding the mechanism of HIV-1 infectivity.Graphical abstractHighlights► A high-throughput method for profiling and quantification of the differentially expressed proteins in saliva samples was developed. ► Identified that DMBT1, S100A7, S100A8, S100A9 and alpha defensin were up-regulated in saliva from HIV-1 seropositive patients. ► Established analytical strategies are translatable to the clinical setting.

We report a unified strategy for the total syntheses of (−)-psychotriasine and (+)-pestalazine B based on the advanced intermediates of 3α-amino-hexahydropyrrolo[2,3-b]indole. To construct these structural motifs, a cascade reaction involving a BINOL-derived phosphoric anion-paired catalyst for enantioselective or diastereoselective azo-coupling/iminium-cyclizations was developed. The remaining key steps of the synthesis involve a sterically hindered amination via hypervalent iodine reagents and the Larock annulation. These transformations enable a general approach to the syntheses of indole alkaloids containing a 3α-amino-hexahydropyrrolo[2,3-b]indole motif and could be further applied to build a natural product-based library.