Peptidomics represents the systematic study of all peptides in a biological sample, distinct from proteomics which focuses on larger proteins.
What Is Peptidomics?
Definition
The comprehensive study of endogenous peptides:
- **Signaling peptides** — Hormones, neuropeptides
- **Degradome** — Protein breakdown products
- **Processed peptides** — Derived from precursors
Peptide vs. Proteomics Boundary
| Feature | Peptidomics | Proteomics |
|---------|-------------|------------|
| Size range | <10 kDa (<50 AA) | >10 kDa |
| Sample prep | No digestion | Tryptic digestion |
| Focus | Native peptides | Protein identification |
| Complexity | Lower | Higher |
Mass Spectrometry Workflow
Sample Preparation
- Critical first step
- Prevents ex vivo degradation
- Common: acid precipitation, heat inactivation
- Ultrafiltration (10 kDa cutoff)
- Removes large proteins
- Enriches peptide fraction
- Solid-phase extraction
- C18 cartridges
- Removes salts, concentrates sample
LC-MS/MS Analysis
- Reversed-phase C18 columns
- Gradient elution
- Separates peptides by hydrophobicity
- Electrospray ionization (ESI)
- High-resolution mass analyzers
- Orbitrap, Q-TOF instruments
- Fragmentation of peptide ions
- Sequence determination
- Database searching
Identification Challenges
Post-Translational Modifications
- Amidation (C-terminal)
- Acetylation (N-terminal)
- Phosphorylation
- Sulfation
- Complicate identification
Database Searching
- Standard protein databases insufficient
- Need peptide-specific databases
- Consider alternative cleavages
Quantification
- Label-free approaches
- Stable isotope labeling
- Multiple reaction monitoring (MRM)
The Human Peptidome
Sources of Endogenous Peptides
1. **Prohormone processing** — Insulin, glucagon, etc.
2. **Neuropeptide processing** — Endorphins, neuropeptide Y
3. **Antimicrobial peptides** — Defensins, cathelicidins
4. **Protein degradation** — MHC peptides, degradome
Size Distribution
- Peak around 1-3 kDa
- Tail to 10 kDa
- Majority under 30 amino acids
Applications
Biomarker Discovery
- Disease-specific peptide profiles
- Cancer markers
- Cardiovascular markers
- Neurological disease markers
Neuropeptidomics
- Brain region-specific analysis
- Signaling pathway studies
- Drug effect monitoring
Clinical Peptidomics
- Urine peptidome (kidney disease)
- Plasma peptidome (cardiovascular)
- CSF peptidome (neurological)
Drug Development
- Target identification
- Mechanism of action
- Biomarker-guided trials
Technical Advances
High-Resolution MS
- Accurate mass determination
- Improved identification confidence
- Better PTM localization
Data-Independent Acquisition (DIA)
- Comprehensive coverage
- Improved quantification
- SWATH-MS approach
Single-Cell Peptidomics
- Individual cell analysis
- Heterogeneity studies
- Emerging capability
