Limitations of Traditional Protein Study Methods
Studying proteins in their native biological context has long been a major challenge in molecular biology. Traditional methods, although widely used, often distort the actual cellular environment and limit functional interpretation. Techniques like antibody-based detection or plasmid-driven overexpression can introduce artifacts and do not allow real-time analysis in living cells.
In this context, the need for tools that enable the observation of proteins as they naturally occur, under physiological conditions, and within live cells is becoming increasingly evident in molecular biology.
CRISPR/Cas9 Knock-In: A New Era for Protein Analysis
The CRISPR/Cas9 system — a revolutionary gene-editing tool that acts as molecular scissors to precisely cut and modify DNA — has transformed how we study proteins by enabling precise knock-in of tags at endogenous genomic loci, preserving natural regulatory elements and maintaining physiological expression levels. This approach minimizes artifacts and allows researchers to monitor protein behavior under native conditions, in real time.
Among the most effective tagging tools for this purpose are HiBiT and NanoLuc® technologies, two bioluminescent systems offering outstanding sensitivity, broad dynamic range, and live-cell compatibility. Two bioluminescent systems offering outstanding sensitivity, broad dynamic range, and live-cell compatibility.
HiBiT is an 11–amino acid peptide that forms an active luciferase when complemented with LgBiT, producing a bright luminescent signal upon substrate addition. Its small size minimizes the risk of interfering with protein function.
NanoLuc® luciferase is a small, highly stable luciferase used as a direct fusion tag. It delivers a high signal-to-background ratio and has become a preferred alternative to traditional firefly luciferase in many applications outlined in the next section.
Key Applications in Drug Discovery
1. Targeted Protein Degradation (TPD) and Real-Time Monitoring
Endogenous tagging with HiBiT enables sensitive quantification of protein abundance with simple add-mix-measure protocols. Compatibility with both endpoint and real-time, live cell methods makes this a versatile tool for studying changes in protein levels and how this occurs dynamically over time. This is especially valuable for evaluating the efficacy of degrader compounds such as PROTACs, under conditions that reflect physiological regulation — avoiding the artifacts often introduced by overexpression models.
2. Protein Trafficking, Secretion, and Structural Studies
The HiBiT system also supports fast, scalable detection of secreted and membrane-bound proteins in live cells, making it ideal for studying protein trafficking, receptor internalization, and ligand-induced endocytosis. These applications are particularly relevant for antibody development and GPCR research — critical areas in drug discovery. Additionally, endogenous tagging facilitates the purification of proteins for advanced structural studies such as single-particle cryo-EM, helping preserve native conformations and protein complexes during isolation.
Implementation Options in the Lab
CRISPR/Cas9-mediated endogenous tagging can be implemented through two main strategies:
- A custom approach, where researchers design target-specific gRNAs and donor templates, followed by clone selection and validation. This route offers maximum flexibility and is well suited for highly tailored experimental needs.
- Or pre-engineered knock-in cell lines, which dramatically reduce timelines by providing validated models for immediate use. These off-the-shelf solutions eliminate weeks — or even months — of development work and allow teams to focus directly on biological questions.
Learn more about available cell lines and custom paths to adoption.
Future Perspectives: Expanding the Potential of Endogenous Tagging
Endogenous tagging is redefining how we approach protein analysis. What was once complex and time-consuming can now be implemented with unprecedented efficiency. As a result, more labs can ask deeper biological questions with tools that reflect native protein dynamics in live cells.
One of the most exciting developments is the integration of artificial intelligence, which is accelerating the design process by predicting optimal knock-in sites and generating optimized gRNAs.
Combined with high-throughput workflows and emerging therapeutic modalities, endogenous tagging is becoming a strategic asset in modern drug discovery.
Conclusion
CRISPR/Cas9-mediated endogenous tagging introduces a revolutionary approach in how proteins are studied. By preserving the genomic and physiological context of protein expression, it provides more accurate, biologically relevant data than traditional overexpression or primary antibody-based methods, while providing the simple, quantitative detection methods. Tools like HiBiT and NanoLuc® are accelerating this shift, offering unmatched sensitivity, scalability, and flexibility across diverse applications.
Want to see how we have used this technique to build a catalog of available cell lines or get information on how to do it yourself? Learn more
References:
- Doudna & Charpentier (2014). CRISPR-Cas9 Genome Engineering. Science, 346(6213), 1258096.
- Schwinn, M.K., et al. (2018). CRISPR-Mediated Tagging of Endogenous Proteins with a Luminescent Peptide. ACS Chemical Biology, 13(2):467-474.
- Schwinn, M.K., et al. (2020). A Simple and Scalable Strategy for Analysis of Endogenous Protein Dynamics. Scientific Reports, 10:8953.
- Blog: CRISPR/Cas9 Knock-In Tagging: Simplifying the Study of Endogenous Biology – Promega Connections (2020).
- Blog: CRISPR/Cas9 HiBiT Knock-In: A Scalable Approach for Studying Endogenous Protein Dynamics – Promega Connections (2020).
Teresa Simon
Latest posts by Teresa Simon (see all)
- CRISPR/Cas9 Endogenous Tagging in Drug Discovery - December 16, 2025
