Week 11 HW: Bioproduction & Cloud Labs

Cell-Free Protein Synthesis Lab — Questions & Answers

Q1. Provide a 1–2 sentence description of each component’s role in the 20-hour NMP-Ribose-Glucose master mix.

E. coli Lysate

BL21 (DE3) Star Lysate — Provides the core transcription/translation machinery (ribosomes, tRNAs, aminoacyl-tRNA synthetases, initiation/elongation/release factors, and metabolic enzymes). The “Star” strain carries an RNase E mutation that stabilizes mRNA, and the (DE3) lysogen supplies T7 RNA Polymerase for high-level transcription from T7 promoters.

Salts / Buffer

  • Potassium Glutamate — Supplies $\text{K}^+$ ions critical for ribosome assembly, tRNA binding, and translation fidelity; glutamate is the preferred counter-ion because $\text{Cl}^-$ inhibits many lysate enzymes.
  • HEPES-KOH pH 7.5 — A zwitterionic buffer that holds the reaction near physiological pH, preventing acidification as glycolysis and ATP hydrolysis generate protons over the long incubation.
  • Magnesium Glutamate — $\text{Mg}^{2+}$ is an essential cofactor for RNA polymerase, ribosomes (stabilizes rRNA tertiary structure and the small/large subunit interface), and virtually every NTP-using enzyme in the system.
  • Potassium Phosphate Monobasic / Dibasic (1.6:1 ratio) — Provides inorganic phosphate ($\text{P}_\text{i}$) that feeds substrate-level phosphorylation in glycolysis to regenerate ATP from ADP, while the dibasic:monobasic ratio sets the buffering pH.

Energy / Nucleotide System

  • Ribose — Phosphorylated by ribokinase to ribose-5-phosphate, which feeds the pentose phosphate pathway and serves as a precursor for nucleotide salvage / regeneration of NTPs from NMPs.
  • Glucose — The primary carbon and energy source; glycolysis converts it to pyruvate, generating ATP and NADH that drive sustained energy regeneration over the 20-hour reaction.
  • AMP, CMP, UMP — Nucleoside monophosphate precursors that endogenous kinases (NMP and NDP kinases) phosphorylate to ATP, CTP, and UTP for transcription; cheaper and more stable than supplying NTPs directly.
  • GMP — Listed at 0 mM in this recipe; GTP is instead generated from guanine via the salvage pathway, avoiding the cost of GMP and reducing inhibitory phosphate accumulation.
  • Guanine — Converted to GMP by HPT (hypoxanthine/guanine phosphoribosyltransferase) using PRPP, then phosphorylated to GTP for transcription and translation (GTP powers initiation, elongation, and release).

Translation Mix (Amino Acids)

  • 17 Amino Acid Mix — Supplies 17 of the 20 proteinogenic amino acids used as substrates by aminoacyl-tRNA synthetases to charge tRNAs for protein synthesis.
  • Tyrosine (pH 12) — Tyrosine is poorly soluble near neutral pH, so it is prepared in a high-pH stock and added separately to ensure it stays in solution at the correct concentration.
  • Cysteine — Added separately because cysteine readily oxidizes to cystine (and forms disulfides), so it requires its own fresh stock to deliver reduced, usable amino acid into the reaction.

Additives

  • Nicotinamide — Precursor for $\text{NAD}^+/\text{NADH}$ regeneration via the salvage pathway; $\text{NAD}^+$ is essential for the GAPDH step of glycolysis, which is required for ATP regeneration from glucose during the long incubation.

Backfill

  • Nuclease-Free Water — Brings the reaction to final volume while ensuring no contaminating RNases or DNases degrade the DNA template, mRNA, or tRNAs during the extended incubation.

Q2. Describe the main differences between the 1-hour PEP/NTP and 20-hour NMP-Ribose-Glucose master mixes (2–3 sentences).

The PEP/NTP system is engineered for speed: it directly supplies the four high-energy NTPs (ATP, GTP, CTP, UTP) plus phosphoenolpyruvate (PEP-Mono) and maltodextrin as fast-discharging energy donors, giving an immediate burst of transcription and translation that runs out within ~1 hour. The NMP-Ribose-Glucose system instead supplies cheap low-energy precursors (NMPs, ribose, glucose, guanine) and lets the lysate’s native metabolism — glycolysis fueled by phosphate buffer and $\text{NAD}^+$ regenerated from nicotinamide — slowly regenerate NTPs over ~20 hours, trading peak rate for sustained yield, lower cost, and avoidance of inhibitory byproducts like accumulated phosphate. As a result, the 1-hour mix also relies on extra small-molecule boosters (spermidine, DMSO, cAMP, NAD, folinic acid) to maximize a short burst, while the 20-hour mix’s design philosophy is metabolic self-sufficiency for long-running, sustainable protein production.

Q3. Identify and explain at least one biophysical or functional property of each of the six fluorescent proteins that affects cell-free expression or readout (1–2 sentences each).

1. sfGFP (superfolder GFP) — Engineered specifically for rapid, robust folding (maturation ~14 min) even when fused to misfolded partners, which makes it nearly ideal for CFPS where lysate chaperone capacity is limited. Like all Aequorea-lineage GFPs, however, chromophore maturation requires molecular oxygen, so sealed/anaerobic reaction wells will cap final fluorescence regardless of how much protein is translated.

2. mRFP1 — A first-generation monomeric DsRed derivative with slow, two-step oxygen-dependent maturation (on the order of ~1 hour or more), meaning a substantial fraction of translated mRFP1 in a short cell-free run will be present but non-fluorescent. It is also moderately acid-sensitive ($\text{p}K_a \approx 4.5$) and the dimmest of the six (low quantum yield ~0.25), so pH drift and incomplete maturation both suppress readout.

3. mKO2 — A monomeric coral (Fungia) FP with reasonably fast maturation (~30–60 min) and good photostability, but it is acid-sensitive ($\text{p}K_a \approx 5.5$): as glycolysis acidifies the CFPS reaction over 36 hours, mKO2 fluorescence is progressively quenched even if protein levels keep rising. Like all Anthozoa-derived FPs, its red-shifted chromophore requires a second oxidation step that consumes $\text{O}_2$.

4. mTurquoise2 — Aequorea-lineage cyan FP with the highest quantum yield among CFPs (~0.93), fast maturation, and excellent pH stability ($\text{p}K_a \approx 3.1$), so per-molecule readout is very strong and largely insensitive to reaction acidification. Folding is efficient in E. coli lysate, making it one of the most “forgiving” reporters for cell-free conditions.

5. mScarlet-I — A synthetic-template monomeric red FP whose “I” variant trades a small drop in quantum yield for dramatically faster maturation (~36 min vs. ~174 min for mScarlet), which is critical in CFPS where you want signal accumulation to track translation rather than lag behind it. It is still $\text{O}_2$-dependent (two-step Anthozoa-type chromophore) and benefits from sustained energy regeneration over long incubations.

6. Electra2 — A 2022 blue FP derived from mRuby3 (Anthozoa/eqFP611 lineage), engineered via dual bacterial+mammalian screening for high intracellular brightness and efficient folding in the E. coli cytoplasm — directly relevant to lysate-based CFPS. It inherits the two-step oxygen-dependent maturation of its Anthozoa parent, so $\text{O}_2$ availability and incubation time both gate final readout.

Q4. Create a hypothesis for how adjusting one or more reagents in the cell-free master mix could improve a specific biophysical or functional property identified above, over a 36-hour reaction.

Protein: mRFP1 Reagent change: Increase HEPES-KOH (pH 7.5) from 45 mM to ~80 mM (matching the 1-hr PEP/NTP mix), and slightly raise Magnesium Glutamate from 7.0 mM toward ~8–9 mM.

Rationale / expected effect: mRFP1’s two limiting properties in CFPS are slow oxygen-dependent maturation and moderate acid sensitivity. Over 36 hours, glycolysis of the supplied glucose/ribose accumulates pyruvate, lactate, and inorganic phosphate, dropping the reaction pH — which both quenches the existing mRFP1 chromophore (acid $\text{p}K_a \approx 4.5$) and slows the late oxidation step of chromophore maturation, which proceeds best near neutral pH. Raising HEPES nearly doubles buffering capacity so the reaction stays close to pH 7.5 deep into the incubation, preserving fluorescence of already-matured mRFP1 and giving the slow-maturing fraction the neutral-pH window it needs to finish oxidizing. The small $\text{Mg}{2+}$ bump compensates for additional $\text{Mg}{2+}$ chelation by the higher buffer/phosphate load and keeps ribosomes and NMP/NDP kinases active, so translation continues feeding new mRFP1 molecules into that maturation pipeline through the full 36 hours rather than stalling at hour ~10–15.

Proposed control: Test the elevated-HEPES condition against mTurquoise2 (pH-stable, fast-maturing) in parallel — if the hypothesis is correct, the buffer boost should help mRFP1 substantially more than mTurquoise2, isolating the pH/maturation effect from a generic translation-yield effect.