# Cell Free Protein Expression with Strep-tag Purification and Yield via A280

**URL:** https://cloud.ginkgo.bio/protocols/cfps-strep-tag-purification-a280
**Status:** Ginkgo Certified
**Price:** $149/sample
**Turnaround:** up to 11 days
**Throughput:** Up to 88 constructs per run (1 column reserved for controls), 96-well format

## Overview

End-to-end automated expression and purification of StrepII-tagged proteins. Linear DNA templates are expressed in 100 uL CFPS reactions for 20 hours, purified with StreptactinXT magnetic beads on the Agilent Bravo, and quantified from the eluate by A280 absorbance on the BMG PHERAstar. Purity and size assessment are performed on the Revvity LabChip. Enables rapid, data-driven assessment of expressibility before larger-scale campaigns.

## Input

- **DNA Input:** Linear DNA sequence
- **Tag Orientation:** N-terminal or C-terminal Strep-II tag fusion (validated with C-terminal tags; success is protein-dependent)
- **Format:** Up to 88 constructs per run, 1 column of wells for controls

## Output

- **Yield Quantification:** A280 per well, converted to protein concentration (mg/mL) via the protein's molar extinction coefficient
- **Expression Confirmation:** Fluorescence signal relative to controls
- **Assay Quality Metrics:** Per-run quality summary with plate-level controls

## Automated Workflow

### Phase 1 - CFPS Reaction Setup

1. Stamp DNA into CFPS mix (Agilent Bravo 96)
2. Incubate (Cytomat / Inheco)

### Phase 2 - Mag Bead Purification

1. Dispense reagents and load samples (Biotek / Agilent)
2. Bind sample to beads (Bravo Shaker)
3. Wash beads (Agilent Bravo 96)
4. Elute purified protein (Agilent Bravo 96)

### Phase 3 - Detection & Quantification

1. Transfer eluate to read plate (Agilent Bravo 96)
2. Read A280 & fluorescence (BMG PHERAstar)

## Ordering

- **Number of Proteins:** configurable
- **Number of Replicates:** configurable
- **File Upload:** CSV, Excel, FASTA, TXT, PDF, ZIP
- **Additional Details:** free-text field for special requirements

## Use Cases

- Purified-protein yield quantification from cell-free expression
- Screening Strep-tagged constructs before scale-up
- Comparing expression and purity across sequence variants