A closer look at secretion efficiency in Yarrowia lipolytica (Swietalski et al., 2020)

Overview

Efficient production of recombinant proteins remains a cornerstone of modern biotechnology, underpinning applications across pharmaceuticals, food processing, and industrial biocatalysis. One of the key challenges in this space is not simply producing proteins, but ensuring they are secreted out of the cell, simplifying downstream processing and reducing overall cost.

In this study, Swietalski et al. (2020) explore the secretion capabilities of the yeast Yarrowia lipolytica, with a particular focus on whether protein size influences secretion efficiency, a widely assumed limitation in bioprocessing.

What Was Done?

Researchers engineered Yarrowia lipolytica¹ to produce two different enzymes:

• A smaller enzyme: β-glucosidase²(CelB; 55 kDa))
• A significantly larger enzyme: β-galactosidase³ (M1; 120 kDa)

Both were expressed under identical genetic and process conditions, allowing for a direct, controlled comparison.

The strains were cultivated in bioreactors over 78 hours, with measurements taken throughout to assess:

• Cell growth and biomass
• Total enzyme production
• Distribution between intracellular and extracellular fractions
• Gene expression (mRNA levels)

A critical part of the methodology involved separating what remained inside the cell from what had been successfully secreted. To achieve this, cell pellets were processed using high-pressure cell disruption (Constant Systems OneShot), enabling rapid recovery of intracellular proteins for accurate quantification.

Why Does this research Matter?

In simple terms, the study addresses a key question:

Is it harder for cells to secrete large proteins?

This assumption influences everything from host selection to process design in industrial biotechnology. If true, it would limit the types of proteins that can be efficiently produced using secretion-based systems.

What are some key findings of the study?

1. Bigger Proteins Are Not Necessarily Harder to Secrete

Contrary to expectation, the larger enzyme (M1, 120 kDa) was less abundant overall, but far more efficiently secreted (~85%)

Whereas the smaller enzyme (CelB, 55 kDa) was produced in much higher quantities but largely remained trapped inside the cell (~73%)

Therefore, protein size alone does not dictate secretion efficiency.

2. Production and Secretion Are Separate Bottlenecks

The study revealed that:

• CelB showed strong gene expression and protein production - but poor secretion
• M1 showed high gene expression - but limited translation and lower total yield

This highlights a crucial concept: Protein production and protein secretion are governed by different biological constraints

In other words, optimising one does not guarantee success in the other.

3. Intracellular Accumulation Reveals Process Limitations

The accumulation of CelB inside the cell suggests a bottleneck in the secretory pathway, likely during transport through the cell’s internal machinery (ER → Golgi → membrane).

Without accurately measuring intracellular protein levels, this limitation would not have been visible.

4. Yarrowia lipolytica Shows Strong Potential as a Secretion Host

Despite lower overall production of M1, the yeast demonstrated the ability to efficiently secrete large, complex proteins (>100 kDa)

This positions Y. lipolytica as a promising alternative to more traditional hosts such as Saccharomyces cerevisiae, particularly for applications requiring secretion of larger biomolecules.

A practical note on measurement: Why does cell disruption Matter?

A key (though often overlooked) aspect of this study is how intracellular protein levels were quantified.

To distinguish between what was secreted and what remained inside the cell, the researchers used high-pressure cell disruption to break open yeast cells and recover soluble intracellular proteins prior to analysis.

This step is essential because yeast cells have notoriously robust cell walls, making efficient lysis non-trivial. Furthermore, accurate mass balance (intra vs extra) depends on complete and reproducible cell disruption, whilst the enzyme activity must be preserved for meaningful comparison

In this case, the use of high-pressure disruption enabled reliable recovery of intracellular enzymes, supporting the study’s central conclusion around secretion efficiency.

What does this mean for Bioprocessing?

From an industrial perspective, this study reinforces several important principles:

• Secretion efficiency must be evaluated, not assumed
• Protein-specific optimisation is essential - one system does not fit all
• Analytical accuracy is critical when assessing intracellular vs extracellular yields

Perhaps most importantly:

A protein that is easy to produce is not necessarily easy to secrete, and vice versa

Final Thoughts

This work provides valuable insight into the complexity of protein secretion in yeast systems. By decoupling production from secretion, it challenges conventional assumptions and highlights the need for a more nuanced approach to host selection, secretion analysis, and overall process optimisation.

The study also reinforces the importance of understanding not only what is successfully secreted, but what remains intracellular. In this case, high-pressure cell disruption using the Constant Systems OneShot enabled reliable recovery and accurate quantification of intracellular protein, helping the researchers build a more complete picture of secretion efficiency and overall process performance.

More broadly, the paper serves as a reminder that robust analytical methods, including effective and reproducible cell disruption, are fundamental to generating meaningful biological insight and advancing bioprocess understanding.

This article was written by Matt Wright, Technical Account Manager at BPES

Reference Swietalski et al. Microb Cell Fact (2020) Secretion of a low and high molecular weight β‑glycosidase by Yarrowia lipolytica

Footnotes:

1. Yarrowia lipolytica is an unconventional, oleaginous yeast recognised as a safe (GRAS) biotechnological "workhorse" for industrial production of lipids, enzymes, and proteins. It is extensively used to produce food additives, biofuels, and nutritional supplements due to its ability to consume unconventional carbon
2. β-glucosidases are an essential class of enzymes found in all domains of life that catalyse the hydrolysis of glycosidic bonds to release glucose. They are often the rate-limiting step in the breakdown of cellulose, converting the disaccharide cellobiose into individual glucose units.
3. β-galactosidase an essential enzyme responsible for the cleavage of terminal non-reducing -D-galactose residues, most notably hydrolysing lactose into glucose and galactose.