Combination of extraction tip and MALDI-TOF-MS for efficient separation and analysis of cysteine-containing peptides

Non-tapered PTFE capillary as robust and stable nanoelectrospray emitter for electrospray ionization mass spectrometry

RATIONALE

The successful implementation of electrospray ionization mass spectrometry (ESI-MS) largely relies on the physical and chemical properties of electrospray emitters. Current ESI emitters based on pulled glass or fused-silica capillaries suffer from complicated fabrication procedures and short lifetime because of clogging and breakage problems. ESI emitters with high robustness, easy operation, and low cost are in great demand.

METHODS

We proposed to directly use non-pulled and non-tapered polytetrafluoroethylene (PTFE) capillaries as nanoelectrospray emitters. We evaluated and studied the performance of PTFE emitters under different flow rates and ESI voltages. Their applications in direct infusion and liquid chromatography (LC)-MS analysis were achieved.

RESULTS

High stable electrospray (relative standard deviation of total ion current intensity <5%) can be obtained at flow rates from 100 nL/min to 1500 nL/min and at ESI voltages from 1.8 kV to 2.9 kV using non-tapered PTFE emitters. Different types of samples including small-molecule drugs, peptides, and proteins can be detected with high sensitivity. LC-MS analysis of two model peptides was successfully demonstrated.

CONCLUSIONS

We have demonstrated that a non-tapered PTFE capillary can be a promising ESI emitter for both direct infusion and LC-MS analysis. We envision it could find broad applications in high-throughput MS analysis fields, such as drug screening and proteomics, where robust and reproducible operations are essentially required. Copyright © 2016 John Wiley & Sons, Ltd.

Identification of single amino acid substitutions (SAAS) in neuraminidase from influenza a virus (H1N1) via mass spectrometry analysis coupled with de novo peptide sequencing

RATIONALE

Amino acid substitutions in the neuraminidase of the influenza virus are the main cause of the emergence of resistance to zanamivir or oseltamivir during seasonal influenza treatment; they are the result of non-synonymous mutations in the viral genome that can be successfully detected by polymer chain reaction (PCR)-based approaches. There is always an urgent need to detect variation in amino acid sequences directly at the protein level. Mass spectrometry coupled with de novo sequencing has been explored as an alternative and straightforward strategy for detecting amino acid substitutions, as well - this approach is the primary focus of the present study.

METHODS

Influenza virus (A/Puerto Rico/8/1934 H1N1) propagated in embryonated chicken eggs was purified by ultracentrifugation, followed by PNGase F treatment. The deglycosylated virion was lysed and separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The gel band corresponding to neuraminidase was picked up and subjected to liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis.

RESULTS

LC-MS/MS analyses, coupled with manual de novo sequencing, allowed the determination of three amino acid substitutions: R346K, S349 N, and S370I/L, in the neuraminidase from the influenza virus (A/Puerto Rico/8/1934 H1N1), which were located in three mutated peptides of the neuraminidase: YGNGVWIGK, TKNHSSR, and PNGWTETDI/LK, respectively.

CONCLUSIONS

We found that the amino acid substitutions in the proteins of RNA viruses (including influenza A virus) resulting from non-synonymous gene mutations can indeed be directly analyzed via mass spectrometry, and that manual interpretation of the MS/MS data may be beneficial. Copyright © 2016 John Wiley & Sons, Ltd.