Producing and Characterizing a Heterotrimeric Protein Complex for Screening and Biophysical Studies

The Challenge

A client required both biotinylated and non-biotinylated forms of a heterotrimeric protein complex to support screening and biophysical characterization activities.

The target complex is involved in tumor suppression and was used to support the identification of novel targeted therapeutic approaches. The project required successful co-expression of three proteins, purification of the assembled complex, generation of two different protein formats, and confirmation that the final products met the quality requirements for downstream studies.

Our Approach

Proteins A and B were co-expressed from a pETDuet expression vector, while Protein C was co-expressed from a separate pET28 construct as part of a strategy to produce the target heterotrimeric complex.

The expression strategy incorporated:

• An AviTag sequence at the C-terminus of Protein A to enable site-specific biotinylation.
• An N-terminal 6His-TEV tag on Protein C to support purification and subsequent tag removal.
• Co-expression of all three proteins in E. coli to promote assembly of the heterotrimeric complex during production.

Following expression, the complex was purified using nickel affinity chromatography and the 6His tag was removed using TEV protease. Additional purification steps included:

• Subtractive chromatography
• Ion exchange chromatography
• Size exclusion chromatography

Once the purified complex had been obtained, a portion of the material was biotinylated using biotin ligase and subsequently re-purified.

Confirming Complex Formation

Producing individual proteins is often only one part of the challenge.

SDS-PAGE analysis showed the presence of all three protein components following purification, supporting successful co-expression and recovery of the heterotrimeric complex.

SDS PAGE and analytical size exclusion data confirmed that we had purified the heterotrimeric complex.

Protein Characterization by Mass Spectrometry

Mass spectrometry was used throughout the workflow to verify the identity and integrity of the proteins at each stage of the process.

Using LC-MS analysis, the team was able to:

• Confirm the molecular masses of all three protein components.
• Verify successful removal of the 6His tag from Protein C following TEV cleavage.
• Confirm site-specific biotinylation of Protein A through detection of the expected mass increase.

Analysis demonstrated a mass increase of approximately 226 Da following biotinylation, consistent with the addition of a single biotin molecule to the AviTag sequence.

Outcome

Using the optimized workflow, approximately 30 mg/L of purified heterotrimeric complex was produced.

The initial feasibility study successfully generated more than 5 mg of both biotinylated and non-biotinylated protein complex within a short project timeline, providing the client with material suitable for screening and biophysical applications.

Comprehensive analytical characterization confirmed:

• Successful co-expression of all three proteins.
• Formation of the heterotrimeric complex.
• Efficient removal of purification tags.
• Successful site-specific biotinylation.

This combination of protein production, purification, functionalization, and analytical characterization provides confidence that final protein preparations are suitable for downstream studies.

Why It Matters

Many drug discovery programs rely on protein complexes rather than individual proteins. Producing these assemblies can require coordinated expression, careful purification strategies, and robust analytical characterization to confirm that the final material accurately reflects the intended biological system.

This project demonstrates Sygnature Discovery’s ability to support complex protein production programs by combining:

• Multi-protein expression strategies
• Protein purification expertise
• Site-specific protein modification
• Advanced analytical characterization

to generate high-quality protein reagents for screening and biophysical research.

Key Results

✅ Successful co-expression and purification of a heterotrimeric protein complex

✅ Generation of both biotinylated and non-biotinylated protein formats

✅ Approximately 30 mg/L purified complex produced

✅ Greater than 5 mg of each final protein format supplied

✅ Mass spectrometry confirmation of complex integrity, TEV cleavage, and biotinylation

✅ Material delivered to support screening and biophysical studies