What Are BioPROTACs?

A bioPROTAC is a genetically encoded protein that eliminates a specific target protein from inside a cell. Instead of blocking a protein's function with a drug, a bioPROTAC hijacks the cell's own disposal system — the ubiquitin-proteasome pathway — and redirects it to destroy the target protein entirely.

The name borrows from PROTAC (proteolysis-targeting chimera), the small-molecule technology that pioneered this "targeted degradation" approach. But where a conventional PROTAC is a synthesized chemical, a bioPROTAC is a protein — designed, expressed, and delivered like any other biologic. That distinction matters more than it sounds, because it's what lets bioPROTACs reach targets small molecules physically cannot.

The Problem: Why Some Proteins Are "Undruggable"

Most drug discovery still depends on finding a pocket — a groove on a protein's surface that a small molecule can wedge into and block. It works well when a pocket exists. It doesn't work at all when one doesn't.

A large share of disease-relevant proteins have no such pocket. Scaffolding proteins, transcription factors, and many regulatory proteins interact with their partners across broad, shallow surfaces rather than deep binding sites. No pocket means no small molecule, which means the target gets labeled "undruggable" and, for decades, effectively shelved. Targeted protein degradation reframes the problem: instead of asking "can we block this protein's active site," it asks "can we get this protein tagged for destruction." The second question doesn't require a pocket — it requires a way to physically associate with the target long enough to flag it for removal.

How BioPROTACs Work

The ubiquitin-proteasome system, briefly

Every cell already runs a built-in disposal pipeline: proteins tagged with a small marker called ubiquitin get pulled into the proteasome and broken down. This happens constantly, to thousands of proteins, as routine cellular housekeeping. Targeted degradation doesn't invent a new mechanism — it redirects this existing one toward a target protein that wouldn't normally be tagged.

Binder domains vs. small-molecule warheads

A conventional PROTAC uses two chemical "warheads" joined by a linker: one grabs the target protein, the other recruits an E3 ligase — the enzyme that attaches the ubiquitin tag. A bioPROTAC replaces the target-binding warhead with a genetically encoded binder domain — a DARPin, a nanobody, or a peptide — fused directly to an E3 ligase or ligase-recruiting domain. Because these binders engage broad protein surfaces rather than deep pockets, they can target proteins a small molecule never could.

Why genetic encoding changes the economics

A small-molecule PROTAC has to survive a lengthy chemistry optimization campaign: synthesize a candidate, test it, adjust the linker, resynthesize, retest. A bioPROTAC is a sequence. Changing the binder domain or the ligase is a design change, not a synthesis campaign — which means many more candidates can be generated and tested per cycle, and iteration happens in software and cell-based assays rather than in a chemistry lab.

BioPROTAC vs. PROTAC vs. Molecular Glue

All three are targeted protein degraders. They differ in what does the targeting and how it's delivered.

How BioPROTACs Are Designed and Validated Today

Designing a bioPROTAC starts with the target's structural data and ends with a validated, sequence-complete construct — but getting from one to the other requires closing the loop between computation and biology, not stopping at a prediction.

The process runs in three stages. First, generative AI models take the target's structure and produce a large pool of candidate binder-ligase constructs — tens of thousands of sequence variants in a single cycle. Second, those candidates move into wet-lab screening: high-throughput FACS (fluorescence-activated cell sorting) tests each candidate in living cells, measuring which constructs actually bind the target and drive degradation — not just which ones look promising on paper. Third, the surviving candidates are packaged into a lead deliverable with binding and safety data attached.

This matters because a computational prediction and a working degrader are not the same thing. A model can score a sequence as a strong binder; only a cell-based assay confirms it behaves that way inside a real biological system, with real folding, real expression, and real off-target exposure. Skipping that step means shipping a prediction, not a lead.

Proof It Works

Design volume and validation rigor are only useful if they produce results that hold up. On a real discovery program targeting CDC20, this dry-lab-to-wet-lab process generated over 100,000 candidate sequences in a single cycle and delivered a validated degrader with 150.4 pM binding affinity — a tight, cell-confirmed measurement, not a modeled estimate.

Separately, structural predictions from the design models have been benchmarked against experimentally solved structures at 0.72 Å precision, indicating the computational stage is producing structurally accurate candidates before they ever reach the bench. Together, these numbers describe a pipeline that can generate at scale and still validate to a standard that holds up under direct measurement.

Who Uses BioPROTAC Platforms

BioPROTAC discovery shows up in a few recurring situations. Biotech and pharma R&D teams turn to it when a priority target has been deprioritized as undruggable and inhibitor-based approaches have stalled. Academic protein research labs use it to probe protein function by degrading a target of interest and observing the phenotype. And business development teams evaluate bioPROTAC platforms when deciding whether to build discovery capability in-house, license a platform, or co-develop a specific asset with a partner.

FAQ