Week 3 HW: 🧪 Cell-Free Protocols

🧪 Section A: Compare Cell-Free Reaction Compositions

🧂 A1. Why do the concentrations of potassium glutamate and magnesium glutamate differ between compositions? Which is more sensitive?

Potassium glutamate functions to reproduce the intracellular environment of E.coli by contributing to the ionic environment. Magnesium glutamate’s role is for magnesium to interact with the negatively charged phosphate groups in nucleic acids, as well as playing a role in the activity + stability of transcription and translation machinery. Despite this, too much magnesium can reduce protein synthesis; therefore, its concentration must be optimized rather than just increased.

The concentrations of potassium and magnesium glutamate differ between compositions, as the optimum depends on the general chemical environment of the reaction, including the lysate, nucleotide concentrations, energy system, and other salts. Changing one component can change the optimum for another component. In fact, Mg-glutamate and K-glutamate have been shown to interact, meaning that the effect of potassium glutamate can depend on the magnesium concentration.

🔎 Which one is more sensitive?

I would consider magnesium glutamate to be more sensitive, as small changes in magnesium availability have a greater effect on transcription and translation compared to small changes in potassium, whose function is mainly to establish the ionic environment.

⚡ A2. How is a PEP + NTP formulation different from a Ribose + NMP formulation?

Their main difference is in how the reaction supplies the energy and nucleotides necessary for transcription and translation.

🔋 PEP + NTP

PEP is phosphoenolpyruvate, which acts as a phosphate source for ATP generation and NTPs are nucleotides such as ATP, CTP, etc.

The ATP regenerated with the aid of PEP is needed to provide energy for protein synthesis, while the NTPs are used for RNA synthesis. The advantages of using PEP + NTP is that it provides a direct source of energy and NTPs, however, it’s costly, as PEP is relatively expensive. PEP can also result in phosphate accumulation during the reaction, Jewett and Swartz observed that PANOx-SP accumulated substantial phosphate during the reaction, which can eventually inhibit CFPS.

🌱 Ribose + NMP

This formulation uses a different strategy, nucleotides are supplied in the cheaper monophosphate form rather than as triphosphates and ribose provides carbon that can be processed by the lysate. The NMPs are converted into their respective triphosphate forms by enzymes already present in the lysate.

Olsen et al. showed that an optimized formulation could produce NTPs from nitrogenous bases and ribose, allowing the system to rely less on expensive preformed nucleotide triphosphates and phosphorylated energy substrates.

🧬 A3. Comparison of two literature cell-free reaction compositions

For this comparison, I chose:

  1. PANOx-SP from Jewett & Swartz (2004)
  2. RFopt from Olsen et al. (2026)

🔬 Main differences

  1. Energy source: PANOx-SP uses 33 mM PEP, whereas RFopt removes PEP and instead uses ribose and glucose. This is one of the most important differences because PEP is an expensive phosphorylated energy substrate. Olsen et al. specifically aimed to eliminate expensive secondary energy substrates while maintaining high protein production.

  2. Nucleotide source: PANOx-SP directly provides ATP, CTP, GTP, and UTP. RFopt instead provides AMP, CMP, GMP, and UMP and relies on the lysate’s metabolic machinery to generate the NTPs needed for transcription. This is a major cost-saving strategy because it reduces the dependence on expensive NTP reagents.

  3. Magnesium and potassium: PANOx-SP contains 20 mM Mg-glutamate and 175 mM K-glutamate, while RFopt contains 8 mM Mg-glutamate and 362 mM K-glutamate. At first, the RFopt potassium concentration looks high, but this shows that the optimum is specific to the complete reaction composition. Changing the energy and nucleotide systems changes the ionic requirements of the system. Therefore, the optimum salt conditions for one reaction might not be the same for another.

  4. Number of components: PANOx-SP contains many conventional components, including PEP, NTPs, putrescine, spermidine, tRNA, folinic acid, NAD, CoA, and oxalate. RFopt was deliberately simplified to reduce the number of costly reagents.

  5. Cost versus yield: PANOx-SP was a strong-performing formulation, but its reagent cost was high. Olsen et al. experimentally compared formulations and reported a reagent cost of approximately $4,535/L for PANOx-SP versus $143/L for RFopt, with RFopt producing 2.39 ± 0.28 g/L sfGFP under their test conditions.

📚 References

  1. Jewett, M. C., & Swartz, J. R. (2004). Mimicking the Escherichia coli cytoplasmic environment activates long-lived and efficient cell-free protein synthesis. Biotechnology and Bioengineering, 86(1), 19–26. https://doi.org/10.1002/bit.20026
  2. Olsen, M. L., Copeland, C. E., Sundberg, C. A., et al. (2026). Design-driven optimization of low-cost reagent formulations for reproducible and high-yielding cell-free gene expression. Nature Communications, 17, 3478. https://doi.org/10.1038/s41467-026-69605-8
  3. Smith, A. A., Wong, E. L., Donovan, R. C., et al. (2026). Using a GPT-5-driven autonomous lab to optimize the cost and titer of cell-free protein synthesis. bioRxiv. https://doi.org/10.64898/2026.02.05.703998
  4. Koch, M., et al. (2021). Key reaction components affect the kinetics and performance robustness of cell-free protein synthesis reactions. https://doi.org/10.1016/j.ymben.2021.08.005