Week 9 HW: Cell Free Systems

##Part 1 1.Advantages of Cell-Free Over In Vivo Expression Cell-free protein synthesis (CFPS) removes the cell as a “black box” and allows you directly control and observe every variable in real time: pH, redox potential, ionic strength, and cofactor concentration.

2.Main Components and Their Roles

3.Energy Provision and ATP Regeneration

Translation is enormously ATP-hungry: every peptide bond costs ~4 high-energy phosphate bonds. In a tube, the initial ATP pool depletes within 30–60 minutes, stalling ribosomes and collapsing yield.

Phosphocreatine / Creatine Kinase System

ADP + phosphocreatine → ATP + creatine (catalyzed by creatine kinase)

• Add phosphocreatine (~20 mM) and creatine kinase (~0.5 mg/mL).
• Extends productive reaction time from ~1 hour to 3–6 hours.
• Alternative: Maltose/maltodextrin system — a multi-enzyme cascade mimicking glycolysis, cheaper for large-scale reactions.

4.Prokaryotic vs. Eukaryotic Cell-Free Systems

• Prokaryotic Choice — T7 RNA Polymerase: Straightforward cytosolic protein, no PTMs needed, high yield required.
• Eukaryotic Choice — Erythropoietin (EPO): Requires N-linked glycosylation for proper folding. A prokaryotic system would produce misfolded, inactive protein.

Designing Cell-Free Expression of a Membrane Protein

Membrane proteins are hydrophobic — without a lipid bilayer, they aggregate instantly.

Three Solubilization Strategies

1. Detergent micelles (DDM, digitonin) — Simplest; add directly to reaction.
2. Nanodiscs — Pre-assembled lipid bilayer discs; co-translate so protein inserts immediately.
3. Liposomes — Lipid vesicles that capture the protein as it emerges from the ribosome.

##Part 2 Synthetic Minimal Cell: Gut Microbiome Inflammation Sensor

1. Function

1a. What It Does — Input and Output

A liposome-based synthetic cell that detects elevated reactive oxygen species (ROS) in the gut lumen — a molecular signature of intestinal inflammation — and responds by producing and releasing butyrate, a short-chain fatty acid that suppresses NF-κB signaling and restores epithelial barrier integrity.

Analogy: Think of it like a smoke detector hardwired to a fire sprinkler — the same signal that trips the alarm also triggers the response, with no human intervention needed. The synthetic cell is silent in a healthy gut and active only when and where inflammation occurs.

1b. Could Cell-Free Tx/Tl Alone Do This Without Encapsulation?

No. There are three primary reasons:

1. Directionality: Without a membrane boundary, butyrate produced freely in solution would diffuse away immediately with no directional delivery to the epithelium.
2. Protection: The ROS-sensing gene circuit would be exposed to gut proteases and nucleases, degrading within minutes.
3. Threshold Control: There is no mechanism for threshold-gated release — the entire reaction would fire at once rather than responding proportionally to local ROS concentration.

1c. Could a Genetically Modified Natural Cell Do This?

Partially — but with serious limitations compared to a synthetic liposome:

1d. Desired Outcome

A synthetic cell administered orally (enteric-coated capsule) that survives transit to the colon, remains transcriptionally silent in healthy tissue, and activates butyrate synthesis specifically at inflamed foci where $H_2O_2$ exceeds threshold (~50 µM).

2. Component Design

2a. Membrane Composition

The membrane is designed to survive the harsh gut environment (low pH, bile salts) while remaining functional at 37°C.

2b. Encapsulated Contents

The “cytoplasm” of the synthetic cell contains the following:

• Tx/Tl Machinery: E. coli cell-free extract (ribosomes, tRNA, chaperones), T7 RNA Polymerase, and the OxyR-responsive promoter plasmid.
• Pre-loaded Enzymes: Acetyl-CoA acetyltransferase (ThlA) for fast initial response.
• Small Molecules: Acetyl-CoA (2 mM), Phosphocreatine (20 mM) + creatine kinase (0.5 mg/mL), all 20 amino acids (5 mM each), and essential cofactors (NAD⁺/NADH, CoA).

2c. Tx/Tl System Origin: Bacterial (E. coli)

A prokaryotic system is preferred because the OxyR transcription factor and the butyrate synthesis enzymes (from Clostridium) are natively bacterial. No complex post-translational modifications (PTMs) are required, making the high-yield E. coli extract the most efficient choice.

2d. Communication with the Environment

• Sensing (IN — Passive): $H_2O_2$ crosses lipid bilayers freely via passive diffusion. Inside, it oxidizes OxyR, switching it from a repressor to an activator.
• Secretion (OUT — Active): We express VDAC-1 (voltage-dependent anion channel 1). While butyrate is anionic at physiological pH, the expressed VDAC-1 pores permit rapid efflux.

3. Experimental Details

3a. Complete Genes and Lipids

3b. Measuring System Function

Validation is performed through a tiered strategy:

1. Tier 1: ROS-responsive expression: Use a GFP reporter to confirm the OxyR circuit activates at the ~50 µM $H_2O_2$ threshold.
2. Tier 2: Butyrate synthesis: Quantify butyrate production in bulk extract using GC-MS or enzymatic assays.
3. Tier 3: Pore function: Use ANTS/DPX dye efflux assays to confirm VDAC-1 correctly inserts into the liposome membrane.
4. Tier 4: Integrated function: Measure butyrate secretion from encapsulated cells in simulated healthy (5 µM $H_2O_2$) vs. inflamed (100 µM $H_2O_2$) conditions.
5. Tier 5: Bioactivity: Apply the output to Caco-2 cells and measure the reduction in inflammatory markers (IL-8/NF-κB).

##Part 3. Aura-Weave (Smart Medical Wearables)

1. One-Sentence Summary Pitch

Aura-Weave is a smart, disposable textile liner for adult incontinence garments that uses freeze-dried cell-free extracts to seamlessly detect and visually report urinary tract infections (UTIs) by changing color when exposed to infected urine.

2. How the Idea Works in Detail

The Aura-Weave liner features a middle diagnostic layer composed of a highly absorbent cellulose matrix (similar to filter paper). This matrix is pre-loaded with a lyophilized (freeze-dried) cell-free extract (CFE), specific engineered DNA circuits, and pH buffers.

The Mechanism:

1. Dormancy: The system remains completely inactive on the shelf in its dry state.
2. Activation: When the wearer voids urine, the warm liquid acts as the natural rehydration trigger, “booting up” the biological transcription and translation machinery.
3. Detection: If specific UTI biomarkers are present—such as nitrites, leukocyte esterase, or bacterial quorum-sensing molecules—the genetic circuit is triggered.
4. Visual Output: The circuit drives the rapid expression of a vibrant chromoprotein (like AmilCP). Within 45 to 60 minutes, a clear blue warning symbol permeates to the outer visible edge of the textile.

Visual Indicator: A blue symbol or color change alerts the caregiver immediately without requiring a manual diagnostic test.

3. Societal Challenge and Market Need

This addresses the “silent crisis” of UTIs in elderly, bedridden, and cognitively impaired populations (such as those with Alzheimer’s or dementia).

• Communication Barriers: These patients often cannot communicate early symptoms like pain or urgency, leading to delayed diagnosis.
• Medical Risks: Late-stage UTIs frequently progress to severe kidney infections, sepsis, and costly hospitalizations.
• Non-Invasive Monitoring: Aura-Weave eliminates the difficult, messy, and stress-inducing process of collecting a clean urine sample from an uncooperative patient, allowing for continuous, passive health monitoring in nursing homes and home-care settings.

4. Addressing Cell-Free Limitations

Technical Specifications

• Target Biomarkers: Nitrites, Leukocyte Esterase, Quorum-Sensing molecules.
• Reporter Protein: AmilCP (Chromoprotein).
• Time to Result: 45–60 minutes post-activation.
• Storage Requirements: Room temperature (stabilized via Trehalose).

##Part 4

• The Challenge: Current missions detect “bricks” (organic molecules) but not “factories” (active life).
• Strategy: Use FD-CF systems to detect ATP Synthesis and 16S rRNA genes.
• Reasoning: Only active biology synthesizes ATP; abiotic chemistry (like meteorites) might have organics but no coordinated metabolism.
• Experimental Plan: Compare Mars simulant spiked with extremophiles against sterile simulant and abiotic meteorite extracts.