Strategy for isolating and sequencing biologically derived MHC class I peptides

Area of Science:

• Immunology
• Analytical Chemistry
• Proteomics

Background:

• Major histocompatibility complex (MHC) class I peptides on cell surfaces are crucial for mammalian immune responses, particularly the cytolytic T-lymphocyte response.
• Identifying and sequencing these peptides is analytically challenging due to their presence at very low concentrations (10^-15 to 10^-18 M) within complex mixtures.

Purpose of the Study:

• To develop and describe a robust analytical strategy for the identification and sequencing of low-abundance MHC class I peptides.
• To overcome the analytical challenges associated with sequencing minute quantities of peptides from complex biological samples.

Main Methods:

• A two-dimensional chromatography approach was employed, combining reversed-phase high-performance liquid chromatography (RP-HPLC) with on-line membrane preconcentration-capillary electrophoresis-mass spectrometry (mPC-CE-MS).
• Peptides were initially concentrated via immunoaffinity capture, released from the MHC protein complex, and separated by RP-HPLC based on hydrophobicity.
• Subsequent separation by capillary electrophoresis (CE) in the second dimension resolved peptides by charge/mass ratio, followed by tandem mass spectrometry (MS/MS) for sequencing.

Main Results:

• The study successfully demonstrated a strategy for sequencing peptides present in femtomole quantities (< 60 fmol).
• The method was applied to peptides derived from a large number of cells (3.10^9 Kb-derived EL-4 cells), showcasing its sensitivity and applicability to complex biological sources.

Conclusions:

• The described two-dimensional chromatography coupled with mPC-CE-MS/MS provides a powerful and sensitive method for sequencing low-abundance MHC class I peptides.
• This analytical approach significantly advances the ability to study peptide presentation and immune responses at a molecular level.