A new sample preparation method for the absolute quantitation of a target proteome using (18)O labeling combined with multiple reaction monitoring mass spectrometry.

A key step in the workflow of bottom-up proteomics is the proteolysis of proteins into peptides with trypsin. In addition, enzyme-catalytic (18)O labeled peptides as internal standards coupled with multiple reaction monitoring mass spectrometry (MRM MS) for the absolute quantitation of the target proteome is commonly used for its convenient operation and low cost. However, long digestion and labeling times, incomplete digestion and (18)O to (16)O back exchange limit its application, therefore, we developed a rapid and efficient digestion method based on a high ratio of trypsin to protein. In addition, after separation of the digested samples using pipette tips packed with reversed-phase packing materials in house, the trypsin can be separated, collected and reused at least four times. Based on this approach, a novel protein quantification method using (18)O-labeled QconCAT peptides as internal standards combined with MRM MS for the absolute quantitation of a target proteome is established. Experimental results showed that the novel method had high digestion and (18)O labeling efficiencies, and no (18)O to (16)O back-exchange occurred. A linear range covering 2 orders of magnitude and a limit of quantification (LOQ) as low as 5 fmol were achieved with an RSD below 10%. Then, the quantitative method is used for the absolute quantitation of drug metabolizing enzymes in human liver microsomes. The results are in good agreement with the previously reported data, which demonstrates that the novel method can be used for absolute quantitative analyses of target proteomes in complex biological samples.

Preparation of mixed lanthanides-immobilized magnetic nanoparticles for selective enrichment and identification of phosphopeptides by MS.

A new type of mixed lanthanides-immobilized (Tb(3+) , Tm(3+) , Ho(3+) , Lu(3+) ) magnetic nanoparticles, Fe3 O4 @TCPP-DOTA-M(3+) , was prepared with a particle size of approximately 30 nm. A model protein, α-casein, and a protein mixture of α-casein and BSA (1:100) were first used to test the phosphopeptide enrichment efficiency of the newly developed magnetic nanoparticles. For the model protein α-casein, 19 phosphopeptides were identified with the newly developed materials. Even in the tryptic digest of α-casein and BSA (1:100), 16 phosphopeptides were easily detected, suggesting that the novel materials possess high selectivity in phosphopeptide enrichment. To evaluate the phosphopeptide enrichment efficiency in a real biological sample, the materials were used to capture phosphopeptides in the tryptic digests of an extract of HeLa cells. In total, 9048 phosphopeptides corresponding to 2103 phosphoproteins were identified in a single mass spectrometric analysis, indicating the great potential of the new materials for practical applications. Compared with metal oxide-based enrichment methods, the newly developed materials are convenient to prepare and easy to handle, and they save time in the phosphopeptide enrichment procedure, making these materials a good choice for highly selective and sensitive phosphopeptide enrichment in future phosphoproteome analyses.

[A simple preparation method of an electric heating apparatus for heating capillary chromatographic columns and its application in liquid chromatography-mass spectrometry system].

For deep coverage of proteome, especially in performing qualitative identification and quantitative analysis of low-abundance proteins, the most commonly used method is the application of a longer capillary chromatographic column or a capillary column packed with smaller particle sizes. However, this causes another problem, the very high back pressure which results in liquid leaks in some connection parts in a liquid chromatograph. To solve this problem, an electric heating apparatus was developed to raise the temperature of a capillary column for reducing its back pressure, which was further applied in a capillary high performance liquid chromatography-tandem mass spectrometry system (cHPLC-MS/MS), and evaluated in the terms of chromatographic column back pressure and chromatographic column efficiency using bovine serum albumin (BSA) tryptic digests and yeast tryptic digests, separately. The results showed that at the optimum current, our electric heating apparatus could reduce the column pressure of a capillary column packed with 3 µm packing materials by at least 50% during the separation of BSA tryptic digestion and yeast tryptic digestion, compared with that without electric heating. The column efficiency was also increased slightly. This suggested that the electric heating apparatus can significantly reduce the column pressure, which provides an efficient way to use capillary chromatographic columns packed with smaller sizes of particles at a lower pressure.

[Progress in metal-organic frameworks].

Metal-organic frameworks (MOFs) are a class of crystalline materials built from organic binding ligands and metal ions through self-assembly. Currently, MOFs have drawn a growing interest among the scientific teams of various fields. Compared with conventional inorganic porous materials, MOFs possess larger specific surface areas, higher porosity and diversity of structures and functions, thus many potential applications have been proposed in the domains of gas adsorption and separation, sensors, drug delivery, catalysis or others. The combinations of MOFs and other materials such as graphene oxide, magnetic nanoparticles have obvious advantages in adsorption and separation. The appearance of novel materials greatly promotes interdisciplinary developments such as organic chemistry, inorganic chemistry, coordination chemistry, materials chemistry, life science and computer science. This article reviews the progress of MOFs in recent years, including the characteristics of MOFs, advances at home and abroad, applications, central issues of compound MOFs and the prospects in the future.