Week 11-Bioproduction & Cloud Labs
Component‑by‑Component Breakdown
| Component | Role in the Reaction |
|---|---|
| E. coli Lysate – BL21 (DE3) Star Lysate (includes T7 RNA Polymerase) | Provides the cellular machinery (ribosomes, tRNA, enzymes, T7 RNAP) for transcription and translation. The rne131 mutation enhances mRNA stability. |
| Potassium Glutamate | Optimizes ionic strength and mimics the intracellular environment, improving protein yields compared to chloride salts. |
| HEPES-KOH pH 7.5 | Maintains stable pH without precipitating metal ions like Mg²⁺, essential for ribosome function and enzyme activity. |
| Magnesium Glutamate | Mg²⁺ is a cofactor for ribosome assembly, NTP binding, and many enzymes. Glutamate counterion supports native‑like conditions. |
| Potassium phosphate monobasic + dibasic | Secondary buffering system; provides inorganic phosphate for energy regeneration (e.g., from PEP to pyruvate). |
| Ribose | Carbon source for slow energy production via metabolism, sustaining long‑term (20 h) protein synthesis. |
| Glucose | Central energy source; metabolized through glycolysis to generate ATP and NTPs over extended incubation. |
| AMP, CMP, GMP, UMP | Monophosphate nucleotides – precursors for RNA synthesis. The system phosphorylates them to NTPs using endogenous energy. |
| Guanine | Nucleobase precursor for guanine nucleotides via salvage pathways (HGPRT enzyme). Allows transcription even when GMP is omitted. |
| 17 Amino Acid Mix, Tyrosine, Cysteine | Building blocks for the target protein. Tyrosine and cysteine added separately to avoid precipitation. |
| Nicotinamide Backfill | Precursor to NAD⁺, a critical cofactor for glycolysis and energy regeneration. |
| Nuclease Free Water | Solvent; prevents degradation of DNA template and RNA by contaminating nucleases. |
⚡ 1‑Hour Optimized (PEP‑NTP) vs. 20‑Hour (NMP‑Ribose‑Glucose) Master Mixes
| Feature | 1‑Hour Optimized Mix | 20‑Hour Mix |
|---|---|---|
| Nucleotide source | Pre‑assembled NTPs (ATP, GTP, CTP, UTP) | NMPs + guanine (phosphorylated over time) |
| Energy source | PEP (phosphoenolpyruvate) – rapid, direct | Ribose + glucose – metabolized slowly |
| Kinetics | Fast burst of high‑yield synthesis | Sustained production over many hours |
| Best for | Quick protein expression (e.g., screening) | Long‑term, high‑titer expression |
💡 Bonus: How can transcription occur if GMP is not included but guanine is?
Transcription requires GTP. The cell‑free lysate contains the guanine salvage pathway:
- Enzyme hypoxanthine‑guanine phosphoribosyltransferase (HGPRT) transfers a ribose‑phosphate from PRPP (present in the lysate) to the nucleobase guanine.
- This produces GMP (guanosine monophosphate).
- GMP is then phosphorylated to GDP and finally to GTP by endogenous kinases.
Thus, adding only guanine is sufficient to supply all guanine nucleotides for transcription and translation.