Application of a new capillary HPLC- ICP-MS interface to the identification of selenium-containing proteins in selenized yeast

Importance of the Topic

Dietary selenium (Se) is an essential micronutrient with crucial roles in enzyme function and antioxidant defense. Low Se content in many agricultural products can cause widespread deficiencies, prompting the use of Se-enriched yeast as a common supplement. Understanding not only total Se but its specific protein-bound forms is vital for assessing supplement quality and bioavailability.

Objectives and Study Overview

This application study aimed to develop a proteomic workflow that combines capillary HPLC-ICP-MS with LA-ICP-MS mapping and ESI-MS/MS for the selective identification of Se-containing proteins in the insoluble fraction of selenized yeast. By targeting low-abundance Se species, the authors sought to overcome limitations of conventional total Se or water-soluble fraction analyses.

Methodology

The approach consisted of several key steps:

• Sample selection: commercial selenized yeast (2.3 mg Se/g).
• Protein extraction and 2D gel electrophoresis to resolve the insoluble protein fraction.
• LA-ICP-MS imaging to pinpoint high-Se protein spots on the gel.
• In-gel tryptic digestion of selected spots to generate peptide mixtures.
• Capillary HPLC-ICP-MS for Se-specific peptide detection followed by ESI-MS/MS for peptide sequencing and protein identification.

Instrumentation Used

Key instruments included:

• Agilent 1100 capillary HPLC with manual injection valve and Zorbax SB-C18 columns.
• Agilent 7700x ICP-MS with capillary LC interface kit and He collision cell mode.
• ESI LTQ Orbitrap Velos mass spectrometer for high-resolution peptide analysis.

Key Results and Discussion

The workflow successfully detected six Se-containing peptide peaks, five of which were sequenced and matched to selenopeptides of glyceraldehyde-3-phosphate dehydrogenase-3 (GAPDH-3), the predominant Se protein in the insoluble yeast fraction. Selenium incorporation occurred via sulfur-selenium substitution in both methionine and, notably for the first time in yeast, cysteine residues. The method achieved a limit of detection of 0.2 pg Se for isotope 80 under typical gradient conditions.

Benefits and Practical Applications

This capillary HPLC-ICP-MS and proteomics approach offers:

• Enhanced sensitivity for low-abundance Se-peptides.
• Selective mapping and identification of Se-proteins in complex matrices.
• A tool for quality control of Se-enriched supplements and studies of Se bioavailability.

Future Trends and Opportunities

Potential developments include:

• Automation and throughput expansion with microfluidic interfaces.
• Quantitative multi-element speciation in nutritional and environmental samples.
• Extended workflows for clinical biomarkers and broader metalloproteomic applications.

Conclusion

The presented ICP-MS-assisted proteomic platform provides a robust means to identify and characterize Se-containing proteins in selenized yeast, uncovering novel substitution pathways and offering a model for advanced speciation studies in supplement analysis.

References

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3. von Hage J. Proteomics Sample Preparation. Wiley-VCH, Weinheim, 2008.