Optimizing performance of glycopeptide capture for plasma proteomics.

Area of Science:

• Biochemistry
• Analytical Chemistry
• Proteomics

Background:

• Biomarker discovery in complex biological fluids like blood is challenging due to low abundance analytes.
• Selective capture of glycopolypeptides offers a strategy to reduce sample complexity.
• N-linked glycosylation is a common post-translational modification crucial for protein function and disease association.

Purpose of the Study:

• To optimize a protocol for selective capture of N-linked glycopolypeptides from human plasma using magnetic beads and hydrazide chemistry.
• To compare protein-level versus peptide-level glycocapture strategies.
• To evaluate the impact of high-abundance protein depletion on glycoprotein detection sensitivity.

Main Methods:

• Optimization of a magnetic bead-based protocol for N-linked glycopolypeptide capture from human plasma.
• Partial automation using a KingFisher magnetic particle processor.
• Comparison of protein-level and peptide-level capture, and assessment of depleted versus non-depleted plasma.

Main Results:

• An optimized protocol achieved 99% glycopeptide capture specificity with 24% intraday and 30% interday coefficients of variation.
• Depleting 14 high-abundance proteins improved detection sensitivity by approximately one order of magnitude.
• The sensitivity of the method (SPEG) for glycoproteins in depleted plasma was in the 10-100 pmol/mL range.

Conclusions:

• The optimized protocol demonstrates high specificity for N-linked glycopolypeptide capture from human plasma.
• While protein depletion enhances sensitivity, the overall number and sensitivity of detected glycoproteins remain surprisingly limited.
• Further improvements are needed to fully leverage this approach for comprehensive glycoprotein biomarker discovery in plasma.