> ## Documentation Index
> Fetch the complete documentation index at: https://docs.adaptyvbio.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Affinity Tag Purification

> High-throughput protein purification using engineered affinity tags for rapid isolation and concentration

Affinity tag purification is a key step in our protein production workflow, enabling rapid, high-purity isolation of target proteins for downstream assays. Our platform uses two primary affinity tag systems optimized for different experimental requirements.

## Supported Affinity Tags

<CardGroup cols={2}>
  <Card title="Twin‑Strep‑Tag (Default)" icon="dna">
    Our default purification tag due to its high affinity and specificity, enabling excellent yields and clean eluates. Highly interoperable with our BLI/SPR measurements.
  </Card>

  <Card title="Other Tags" icon="tags">
    On demand, we can also work with other tags such as **His**, **Fc**, or lab‑specific alternatives. Tag choice depends on your protein and downstream requirements.
  </Card>
</CardGroup>

## Tag Positioning

**C-terminal placement (default):** We use C-terminal tags for 90% of proteins because the tag only gets expressed if the entire protein gets expressed. This prevents purification of truncated proteins that could occur with N-terminal tags if protein expression stalls.

**N-terminal placement (on request):** Available through the Foundry portal when needed, such as when the binding site is close to the C-terminus and might be affected by tag placement.

All tags include a GS linker for proper spacing and minimal interference with protein function.

## Workflow Integration

Purified proteins from this process are directly used in downstream assays including:

* **Binding assays** (BLI, SPR)
* **Structural analysis**
* **Functional studies**
* **Quality control** measurements

<Note>
  Tag selection and positioning can be customized based on your specific protein and experimental requirements through the Foundry portal.
</Note>