Week 11 HW: Imaging and Measurement

Part B: Cell-Free Protein Synthesis | Cell-Free Reagents

Recording to Gemini：

Component Roles in CFPS

E. coli Lysate (BL21 (DE3) Star): Provides the essential molecular machinery, including ribosomes and chaperones, while the T7 RNA Polymerase drives the transcription of DNA into mRNA.

HEPES-KOH pH 7.5: Functions as a chemical buffer to maintain a stable pH, ensuring that enzymes and proteins remain folded and active throughout the reaction.

Potassium & Magnesium Glutamate: These salts provide the necessary ionic strength; specifically, magnesium is a critical cofactor for ribosome stability and polymerase activity.

Potassium Phosphates: Act as secondary buffers and provide a source of inorganic phosphate required for various metabolic cycles.

Ribose & Glucose: Serve as secondary energy sources that can be metabolized to regenerate ATP and provide carbon backbones for the reaction.

AMP, CMP, GMP, UMP: These are nucleoside monophosphates (NMPs) that serve as the building blocks for RNA synthesis and are phosphorylated into high-energy triphosphates (NTPs).

Guanine: A nitrogenous base that acts as a precursor for GMP, ensuring a steady supply of guanosine nucleotides.

Translation Mix (Amino Acids): Provides the 20 standard building blocks required for the ribosomes to assemble the polypeptide chain of the target protein.

Nicotinamide: Often added as a precursor for NAD +or NADP +, which are essential cofactors for the metabolic pathways that regenerate energy. Nuclease-Free Water: Acts as the solvent for the reaction, ensuring no contaminating enzymes degrade the DNA template or RNA transcripts.

Comparison of Master Mixes

The 1-hour PEP-NTP mix is designed for speed, utilizing high-energy Phosphoenolpyruvate (PEP) and pre-phosphorylated Nucleoside Triphosphates (NTPs) for immediate protein production. In contrast, the 20-hour NMP-Ribose-Glucose mix is built for sustained yield; it uses slower-metabolizing carbon sources and monophosphates (NMPs) to gradually regenerate energy, preventing the rapid inorganic phosphate buildup that typically inhibits shorter reactions.

Bonus: Transcription without GMP

Transcription can still occur because the E. coli lysate contains endogenous enzymes (such as phosphoribosyltransferases) that can salvage the Guanine base. By reacting Guanine with PRPP (phosphoribosyl pyrophosphate), the system can synthesize GMP de novo or through salvage pathways, which is then phosphorylated into the GTP required by the RNA polymerase.

Resource：https://medicoapps.org/m-purine-salvage-pathway/

Part C: Planning the Global Experiment | Cell-Free Master Mix Design

6 Fluorescent Proteins: Biophysical & Functional Properties

1.Fluorescent Protein Property Analysis recording Gemini

sfGFP (superfolder GFP): Exhibits extremely strong folding stability, enabling it to fold correctly and maintain high fluorescence intensity even under rapid synthetic pressure in complex extracellular systems (cell-free systems).

mRFP1: Its main limiting property is oxygen dependence, as chromophore formation requires molecular oxygen, which may lead to limited fluorescence signal in closed 384-well plate reactions.

mKO2: The maturation time of this protein is significantly affected by pH, maturing faster under slightly alkaline conditions, thus requiring a high buffering capacity of the extracellular reaction system.

mTurquoise2: Possesses a high quantum yield, but its folding rate remains the limiting step, making its fluorescence output highly sensitive to translational kinetics.

mScarlet_I: Exhibits strong acid sensitivity; its fluorescence intensity may significantly decrease in the later stages of the reaction when the pH drops due to the accumulation of metabolic byproducts.

Electra2: As an ultra-fast maturation protein, its core advantage lies in its extremely short maturation time, making it ideal for real-time monitoring of protein expression in extracellular systems.

2. Hypothesis for Cell-Free Optimization Since your goal is to maximize fluorescence over a long 36-hour incubation, the primary limiting factors are usually energy depletion and the degradation of the protein’s folding environment.

Protein: sfGFP (Green) Reagent(s): Magnesium Glutamate and Amino Acid Mix. Hypothesis: “By increasing the concentration of Magnesium Glutamate to optimize ribosomal activity and supplementing additional Amino Acids, I aim to extend the metabolic window of the cell-free reaction. Since sfGFP folds rapidly, providing a higher density of building blocks and enzymatic cofactors will maximize the total fluorescence yield over the full 36-hour incubation period.”

4.My Customized 2 μL Supplement Plan:

Selected Protein: sfGFP (Well #98)

Components: 1 μL Magnesium Glutamate + 1 μL Amino Acid Mix.

Reasoning: Since sfGFP is a highly robust folder, the primary limiting factor for a 36-hour incubation is the depletion of building blocks and cofactors. By doubling the available amino acids and increasing magnesium levels (which stabilizes the translation machinery), I expect to maintain a high rate of protein synthesis late into the incubation period, leading to a higher cumulative fluorescence signal compared to the standard mix.

[ { “id”: “nuclease_free_water”, “supplemental_volume_nl”: 1900 }, { “id”: “magnesium_glutamate”, “supplemental_volume_nl”: 50 }, { “id”: “aa_mix_17”, “supplemental_volume_nl”: 50 } ]