Recombinant Peptide Production

Recombinant production complements chemical synthesis, especially for larger peptides and those requiring complex folding.

When to Use Recombinant vs. Chemical Synthesis

Expression Systems

Escherichia coli **Advantages:** - Fast growth (20 min doubling) - High yields (g/L possible) - Well-characterized genetics - Low cost

• No glycosylation
• Limited disulfide formation (cytoplasm reducing)
• Codon bias issues
• Endotoxin removal required

Yeast (Pichia, Saccharomyces) **Advantages:** - Eukaryotic folding machinery - Glycosylation capable - Secretion possible - No endotoxins

• Slower growth than E. coli
• Hyperglycosylation (yeast-specific patterns)
• Lower yields than E. coli

Mammalian Cells (CHO, HEK293) **Advantages:** - Human-like glycosylation - Complex protein folding - Native PTMs

• Slow, expensive
• Lower yields
• Complex media requirements
• Typically for large proteins, not peptides

The Fusion Protein Strategy

Small peptides are often toxic or unstable in bacterial cytoplasm. Solution: express as fusion proteins.

Common Fusion Partners

Advantages - Protect peptide from degradation - Reduce toxicity to host - Improve solubility - Enable affinity purification

Cleavage Strategies

Enzymatic Cleavage

• Sequence: ENLYFQ↓S
• Highly specific
• Works at 4-30°C
• Leaves Ser at N-terminus

• Sequence: IEGR↓
• Well-established
• Can have off-target cleavage

• Recognizes SUMO fold, not sequence
• Leaves native N-terminus
• Highly specific

Chemical Cleavage

• Cleaves after Met
• Harsh conditions
• Must remove internal Met

• Cleaves Asn-Gly bonds
• Specific but limited sites

Intein Technology

Self-Cleaving Inteins - Protein splicing elements - Engineered for controlled cleavage - Generate C-terminal thioesters for NCL

IMPACT System 1. Express peptide-intein-chitin binding domain 2. Purify on chitin resin 3. Induce cleavage with thiol 4. Elute pure peptide

Isotope Labeling

Major advantage of recombinant production:

Uniform Labeling - Grow in ¹⁵N-NH₄Cl, ¹³C-glucose - All residues labeled - Essential for NMR studies

Segmental Labeling - Express labeled + unlabeled fragments - Ligate by NCL or sortase - Simplifies NMR spectra of large proteins

Case Study: Insulin Production

Historical (Before Recombinant) - Extracted from pig/cow pancreas - 8,000 lbs pancreas → 1 lb insulin - Immunogenic in some patients

Recombinant Production - Human insulin gene in E. coli or yeast - Two chains produced separately (A, B) - Refolded and oxidized together - Identical to human insulin