🧬 biology

High-level Expression and Integrated Purification of Recombinant Human Type I+III Collagen in Pichia pastoris

This study establishes a robust, scalable, and cost-effective manufacturing platform for recombinant human type I+III collagen in *Pichia pastoris* by combining multi-copy integration, optimized high-density fermentation at 22°C, and an integrated purification process to achieve high yields (10.42 mg/mL) with ≥94.7% purity and ≥90% activity recovery in a 500 L pilot-scale bioreactor.

Original authors: Lu Li, Yue Huang, Xin Fu, He Xiao, Yun Zhang, Huaiqing Sun, Chaowan Guo, Ying Lin

Published 2026-07-01

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Lu Li, Yue Huang, Xin Fu, He Xiao, Yun Zhang, Huaiqing Sun, Chaowan Guo, Ying Lin

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your skin is a busy construction site. To keep it strong and flexible, it needs two specific types of "steel beams" and "rubber bands" working together: Type I collagen (the strong beams) and Type III collagen (the flexible bands). Usually, these are found together in nature, but making them in a lab has been like trying to build a skyscraper with a wobbly ladder and a broken crane.

This paper describes how a team of scientists built a much better factory to produce these two collagen types together, using a tiny yeast cell as their worker. Here is the story of how they did it, broken down into simple steps.

1. The Worker: A Supercharged Yeast

The scientists chose a tiny yeast called Pichia pastoris to do the heavy lifting. Think of this yeast as a microscopic factory worker.

The Problem: In the past, scientists could only ask the yeast to make one type of collagen at a time, or they got very little product, and it was often messy or broken.
The Solution: They gave the yeast a "super-charged" instruction manual. Instead of giving the yeast just one copy of the recipe for the collagen, they used a special genetic tool (called Cre/loxP) to paste the recipe into the yeast's DNA five times.
The Analogy: Imagine asking a baker to make bread. If you give them one recipe, they make one loaf. If you tape five copies of that recipe to their apron, they suddenly start baking five times as fast. The scientists found that the "5-copy" yeast was the champion, producing the most collagen without getting confused.

2. The Factory Floor: Fermentation

Once they had the super-worker, they needed to feed it and manage the factory floor. They tested this in a small 5-liter tank (like a large kitchen pot) and then scaled it up to a massive 500-liter tank (like a swimming pool).

The Four-Stage Process: They didn't just dump food in and hope for the best. They ran the factory in four strict phases:
1. Growth: Letting the yeast multiply like crazy.
2. Feeding: Giving them a sugar boost (glycerol) to get big and strong.
3. Training: Gently introducing them to their new job (methanol) so they don't get shocked.
4. Production: Turning on the lights to start making the collagen.
The Temperature Trick: The scientists discovered that the yeast worked best when the factory was kept cool. They found that 22°C (about 72°F) was the "Goldilocks" temperature.
- If it was too cold (20°C), the yeast stopped working.
- If it was too warm (25°C), the collagen started to break apart (like chocolate melting in the sun).
- At 22°C, the yeast stayed healthy, and the collagen stayed intact.

3. The Result: A Massive Yield

By using the 5-copy yeast and the perfect temperature, they achieved something impressive. In their giant 500-liter tank, they produced 10.42 mg of collagen per milliliter of liquid.

The Analogy: Think of it like squeezing a sponge. Before, they could only squeeze out a few drops of water. Now, with their new method, they are squeezing out a whole bucket. This is a huge jump in efficiency.

4. The Cleanup: Integrated Purification

Making the collagen is only half the battle; getting it out of the messy yeast soup without breaking it is the other half. Traditional methods are like trying to pick a single red marble out of a jar of mixed marbles using tweezers one by one—it takes forever and you lose most of them.

The New Method: The team built a "conveyor belt" purification system.
1. Clarification: They spun the liquid fast to remove the yeast cells (like a salad spinner).
2. Filtering: They used special filters to catch the collagen while letting the tiny junk pass through.
3. The Magic Magnet (HIC): They used a special column (Hydrophobic Interaction Chromatography) that acts like a magnet. The collagen sticks to it, while the remaining impurities wash away.
4. Final Rinse: They washed off the collagen and removed the salt.
The Outcome: This process was incredibly efficient. They recovered 90% of the collagen they made (very little was lost), and the final product was 94.7% pure. It was clean, strong, and ready to use.

Summary

In short, this paper claims that the team successfully built a reliable, large-scale factory to produce human Type I and Type III collagen together. They did this by:

Giving the yeast five copies of the genetic recipe.
Running the factory at a cool 22°C to prevent breakage.
Using a streamlined cleaning process that keeps the product pure and saves almost all of it.

The result is a stable, high-quality product that mimics the natural mix found in human skin, ready for use in high-end cosmetics and medical materials, all produced without the risks of using animal-derived collagen.

Technical Summary: High-Level Expression and Integrated Purification of Recombinant Human Type I+III Collagen in Pichia pastoris

Problem Statement
Recombinant human type I and type III collagens are critical for skin repair, wound healing, and biomedical applications due to their synergistic effects in natural tissues. However, current production methods face significant bottlenecks:

Limited Synergy: Most research focuses on single-type collagen, failing to replicate the natural coexistence and function of Type I+III.
Low Yield and Scalability: Traditional fermentation often results in low expression yields and unstable processes that hinder scale-up.
Purification Challenges: Multi-step chromatography typically leads to low recovery rates, high costs, and elevated endotoxin levels.
Process Consistency: There is a lack of stable, consistent workflows that can transition smoothly from laboratory to industrial pilot scales.

Methodology
The study developed a comprehensive manufacturing platform utilizing Pichia pastoris GS115, focusing on strain engineering, fermentation optimization, and an integrated purification workflow.

Strain Construction: A codon-optimized fusion gene (WM) encoding human Type I+III collagen was cloned into the pHKA vector under the AOXm promoter with an $\alpha$ CC signal peptide. Using a Cre/loxP-mediated iterative integration system at the Int1 locus, the researchers constructed strains with 1 to 5 copies of the gene. The 5-copy strain was selected for further development after verifying a positive correlation between copy number and expression.
Fermentation Strategy: A four-stage high-density fermentation process was established and scaled from 5 L bench-top to 500 L pilot bioreactors:
1. Batch Growth: 30°C, pH 5.5.
2. Glycerol Feeding: To reach high cell density (OD₆₀₀ ≈ 250).
3. Methanol Adaptation: Gradual increase in methanol feeding at 25°C.
4. Induction Expression: Conducted at an optimized temperature of 22°C to minimize protease degradation.
Integrated Purification: A streamlined workflow was designed to process 500 L fermentation broth:
1. Clarification: Centrifugation followed by 750 kD hollow fiber filtration and 0.45 µm membrane filtration.
2. Buffer Exchange: Ultrafiltration (10 kD) to exchange buffers.
3. Hydrophobic Interaction Chromatography (HIC): Utilizing Phenyl Sepharose 6FF to separate the target protein from impurities.
4. Desalting: Final concentration and desalting via 3 kD ultrafiltration.

Key Results

Strain Performance: SDS-PAGE analysis confirmed that increasing the gene copy number from 1 to 5 significantly enhanced secretory production. The 5-copy strain exhibited the highest expression levels.
Fermentation Optimization: Temperature screening in 5 L bioreactors identified 22°C as the optimal induction temperature. While 20°C failed to trigger effective expression and 25°C resulted in unstable production and degradation, 22°C balanced robust cell growth (maximum OD₆₀₀ of 529) with high-level, intact collagen secretion.
Scale-Up Success: The process was successfully scaled to 500 L with excellent reproducibility across two independent batches. The final expression level reached 10.42 mg/mL.
Purification Efficiency: The integrated purification process achieved a final product purity of ≥ 94.7% with an activity recovery of ≥ 90%. The HIC step effectively removed heterologous impurities while preserving the protein's intact structure, as verified by SDS-PAGE and HPLC.

Significance and Claims
The authors claim to have established a robust, scalable, and cost-effective manufacturing platform for recombinant human Type I+III collagen. Key contributions include:

High-Yield Production: Achieving 10.42 mg/mL in a 500 L bioreactor, a level significantly higher than most reported processes.
Process Stability: Demonstrating a consistent workflow from 5 L to 500 L, addressing the common challenge of scale-up instability.
Efficient Purification: Replacing complex multi-step chromatography with an integrated HIC-based workflow that maintains high recovery (>90%) and high purity (>94.7%) without harsh denaturation.
Industrial Applicability: The resulting product, with its intact structure and high purity, meets the quality requirements for high-end cosmetics and medical materials, offering a safe alternative to animal-derived collagen by avoiding pathogen contamination and immune rejection.