With the advancement of proteolysis-targeting drugs, antibody therapeutics, and target validation studies, researchers have become increasingly focused on… Quantitative analysis of target proteins, protein stability assessment, and dynamic monitoring of protein degradation. The demand is growing ever higher.

Thanks to its small size—comprising only about 11 amino acids—high sensitivity, and the NanoBiT luminescence detection system, HiBiT has become one of the most widely used tags in recent years for protein quantification and proteolysis studies. However, in practical applications, customers often encounter specific challenges:

• Should HiBiT be fused to the N-terminus or the C-terminus of the target protein?
• Should we generate HiBiT-overexpressing cells, or directly perform an in situ HiBiT knock-in?
• Do HiBiT cells necessarily need to express LgBiT?
• Can HiBiT cells be used for PROTAC screening?
• Why does the in situ HiBiT cell construct have a longer construction cycle?

 

In this issue, we will systematically address common challenges in HiBiT cell construction through a Q&A format.

Q1: What is HiBiT, and why is it well-suited for cell line engineering?

HiBiT is an ultra‑small tag in the NanoBiT protein detection system, consisting of 11 amino acids.

When the target protein is fused with HiBiT, it can form a luminescent NanoBiT complex by complementing with LgBiT, thereby converting the expression level of the target protein into a quantifiable luminescent signal.

In simple terms: Target-HiBiT + LgBiT + Substrate → Luminescence

Compared with larger reporter tags such as GFP and NanoLuc, one of HiBiT’s most distinctive features is: The tags are very small, and their potential impact on the target protein’s structure and function is relatively low. Therefore, HiBiT is ideally suited for applications such as quantitative protein expression analysis, studies of protein stability, investigations of protein half-lives, research on protein degradation, PROTAC screening, molecular glue screening, studies of receptor-mediated endocytosis, analyses of membrane protein degradation, and evaluation of antibody therapeutics.

Q2: Why are HiBiT tags well-suited for protein degradation studies?

The central challenge in protein degradation drug development is: how much does the target protein level decrease after treatment with the drug? Traditional methods typically rely on Western blotting to quantify the target protein. However, Western blotting suffers from several limitations: a cumbersome workflow, limited throughput, poor quantitative accuracy, and unsuitability for high‑throughput compound screening. In contrast, HiBiT enables the conversion of target protein levels into a luminescent signal. For example: Target‑HiBiT → addition of a PROTAC → reduction in target protein levels → decline in HiBiT signal → calculation of the extent of protein degradation.

Accordingly, additional parameters can be derived: DC50, Dmax, Emax, the time–response relationship, and the concentration–response relationship. For projects requiring high-throughput screening of numerous compounds, HiBiT offers distinct advantages.

Q3: Should HiBiT be fused to the N-terminus or the C-terminus of the target protein?

This is a very common issue in HiBiT‑based protein engineering. Typically, there is no universally preferred N‑terminal or C‑terminal orientation; the optimal choice must be determined based on the target protein’s structure and function.

N-terminal HiBiT , applicable to proteins that: possess a critical functional domain at the C-terminus; harbor key localization signals at the C-terminus; participate in protein–protein interactions via the C-terminus; or cannot readily be tagged at the C-terminus.

Consumer-facing HiBiT , applicable to: N-terminus with a signal peptide, N-terminus involved in membrane localization, N-terminus possessing critical regulatory functions, and C-terminus relatively exposed with minimal impact on function.

Key considerations during design include:

1) Does the N/C terminus participate in protein function?

2) Does a signal peptide exist?

3) Does a transmembrane structure exist?

4) Whether important structural domains are present;

5) Does a protein degradation signal exist?

6) Does the tag affect protein localization?

7) Does the tag affect protein–protein interactions?

Therefore, prior to formal construction, it is recommended to design the tag placement based on the target protein’s structural domains, subcellular localization, and functional characteristics.

Q4: Does the HiBiT tag require a linker?

It is generally recommended to incorporate a flexible linker, tailored to the characteristics of the target protein. Common strategies include: Target–Linker–HiBiT or HiBiT–Linker–Target. The primary role of the linker is to minimize steric hindrance between the tag and the target protein, particularly for large‑molecule proteins, membrane proteins, multi‑domain proteins, and components of protein complexes.

A well‑designed linker can enhance the detectability of HiBiT while minimizing potential impacts on the target protein’s function. However, longer linkers are not necessarily better; their design should be informed by the structure of the target protein.

Q5: How should one choose between 293-Harbor-HiBiT overexpressing cells and in situ HiBiT cell lines?

This is one of the most critical issues in HiBiT cell engineering. The fundamental distinction between the two strategies can be summarized as follows:

Scheme A: Overexpression of 293-Harbor-HiBiT

By employing a stable integration approach, cells are engineered to constitutively express Target‑HiBiT, yielding the 293‑Harbor‑Target‑HiBiT cell line, which essentially establishes a robust platform for detecting exogenous target proteins.

Scheme B: In situ HiBiT knock-in

Using gene-editing technologies such as CRISPR/Cas9, HiBiT sequences are directly inserted into the endogenous locus of the target gene, generating an Endogenous Target–HiBiT construct. Essentially, this approach tags the native protein within its original genomic context.

How should you choose between the two options?

If the priority is “screening efficiency,” prioritize: 293-Harbor-Target-HiBiT; applicable to: PROTAC primary screening, compound library screening, high-throughput screening, dose‑response experiments, assay development, and preliminary evaluation of protein degradation.

The advantages are: relatively rapid construction, typically high expression levels, and an easily established signal window.

If the focus is on “endogenous biological authenticity,” prioritize: Endogenous Target-HiBiT; applicable to: Endogenous protein expression studies, endogenous protein stability studies, protein half-life studies, PROTAC–mediated endogenous validation, studies on protein degradation mechanisms, and investigations of endogenous signaling pathways.

The advantage is that the target protein remains subject to its native endogenous regulatory mechanisms, thereby more closely mimicking its physiological expression state.

293-Harbor-HiBiT and in situ HiBiT are not a matter of “which is better”; rather, they serve different stages of research.

Q6: Why is the construction of in situ HiBiT‑labeled cells generally more challenging than that of overexpressing cells?

Because in situ HiBiT requires precise tagging of the target gene, the process typically involves: sgRNA design → donor plasmid design → CRISPR-mediated editing → single‑clone screening → genotyping → validation of HiBiT expression → and verification of protein expression and function.

It is particularly important to note that detecting a HiBiT signal does not necessarily mean that the correct in situ HiBiT‑labeled cells have been obtained. Further confirmation is required: the insertion site must be correct, the inserted sequence must be accurate, the junction must be proper, the target protein must be expressed normally, its subcellular localization must show no obvious abnormalities, and its functional activity must remain unchanged. Consequently, in situ HiBiT projects typically demand a more comprehensive validation pipeline.

Q7: Do HiBiT cells necessarily need to stably express LgBiT?

Not necessarily. If a cell‑lysis–based HiBiT assay is used, the assay itself can supply LgBiT and the substrate. Consequently, many HiBiT‑expressing cells do not require additional construction of LgBiT.

If you wish to perform live-cell dynamic imaging, you may consider constructing a system capable of delivering LgBiT into the cell. Therefore, prior to initiating the project, it is essential to first clarify: Do you need endpoint detection, or do you need live-cell dynamic imaging?

Q8: Can HiBiT cells detect membrane proteins?

Yes, and membrane proteins represent one of the most valuable application areas for HiBiT. It can be used to study membrane protein expression, receptor internalization, receptor degradation, antibody binding, antibody‑mediated endocytosis, and receptor stability.

If HiBiT is localized in an extracellular, accessible region, it can also be coupled with appropriate extracellular detection systems for analysis. Consequently, HiBiT holds significant potential for membrane proteins such as GPCRs, RTKs, cytokine receptors, and immune checkpoint proteins.

Q9: Can HiBiT be used for evaluating antibody drugs?

Yes, that’s possible. For example, in a membrane‑bound receptor system—Target‑HiBiT cells—by adding either a blocking antibody or an internalizing antibody, you can assess receptor expression, receptor endocytosis, receptor degradation, and the efficacy of the antibody based on changes in HiBiT signal. Furthermore, by integrating a downstream reporter system, you can establish a multi‑dimensional evaluation framework encompassing binding, internalization, degradation, and functional activity.

Q10: In which drug development scenarios are HiBiT cells suitable?

At present, HiBiT cells are particularly well-suited for the following applications:

Protein degradation

• PROTAC
• Molecular Glue
• Targeted Protein Degradation

 

Antibody drug

• Receptor internalization
• Receptor degradation
• Antibody activity

(Image source: Promega)

 

Protein stability

• Protein half-life
• Protein turnover
• Protein degradation kinetics

 

Target validation

• Target engagement
• Target expression
• Target regulation

 

High-throughput screening

• Compound screening
• Dose-response screening
• Time-course screening

Q11: If a project requires both “high-throughput screening” and “endogenous validation,” how should it be designed?

It is recommended to adopt the “dual-cell model strategy.”

Model 1: 293-Harbor-Target-HiBiT

Position: Screening Cell

Used for:

• Initial compound screening
• PROTAC primary screening
• Dose–response
• Time-effect
• High-throughput screening

 

Model 2: Endogenous Target-HiBiT

Position: Validation Cell

Used for:

• Endogenous protein degradation
• Endogenous expression
• Protein stability
• Mechanism Verification

Ultimately, the workflow takes the form: Screening → Validation → Functional Assay. This design strikes a balance between screening efficiency and biological relevance.

Q12: What strategies can be employed for HiBiT cell line construction at Leman Bio?

Depending on the specific research requirements, two types of core HiBiT cell construct strategies can be provided:

Option 1: 293-Harbor-HiBiT stably expressing cells

Recommended Apps

• PROTAC screening
• Compound screening
• High-throughput screening
• Protein degradation assessment
• Antibody Drug Evaluation

 

Option 2: In situ HiBiT knock-in cells

Recommended Apps

• Endogenous Protein Research
• Protein stability
• Protein half-life
• Endogenous protein degradation
• Mechanism Study

Conclusion

HiBiT is more than just an “11‑amino‑acid tag.” For protein degradation, antibody therapeutics, and target validation, its greater value lies in converting changes in the target protein into rapid, sensitive, and quantifiable cellular signals.

In the construction of HiBiT‑tagged cells, the real challenge is not simply “How do I add the HiBiT tag?” but rather: “What cellular background should be used? What expression strategy? Where should the tag be positioned? And what detection method should be employed?”

 

For most drug screening projects, the following can be given priority:

293-Harbor-Target-HiBiT → High-Throughput Initial Screening

Then through:

Endogenous Target-HiBiT → Endogenous Validation

Finally, in combination:

Western Blot / MS / Functional assay → Multidimensional validation

Thus, a comprehensive HiBiT‑based cellular research platform has been established, spanning from compound screening to mechanistic validation.

 

Liman Bio can, based on the target protein, cellular context, tag placement, and experimental objectives, design for clients either a 293-Harbor stable expression–based or a CRISPR‑mediated in situ HiBiT cell line construction protocol. Supports protein degradation, antibody drug development, and target validation studies.

Welcome, teachers, to reach out with any inquiries!!!