Computer Analysis and Development of Secretory Expression of D-Psicose-3-Epimerase in Escherichia coli

DPEase is the bottleneck

If you make allulose, you know the enzyme story. D-psicose-3-epimerase (DPEase) turns fructose into D-psicose, the sugar we call allulose. It is the catalytic heart of the whole process. But getting enough active, soluble DPEase from E. coli has been the hard part. This paper from the journal Microorganisms shows a practical route: use the right signal peptide, add a little detergent, and drop the temperature.

Background

DPEase is a key enzyme for allulose production. It has been expressed in E. coli with high yield, but high yield inside the cell does not always mean good process economics. When enzyme stays trapped in the cytoplasm, you need cell lysis, centrifugation, and extra purification steps. Secretory expression changes that. If DPEase exits the cell, you can collect it from the culture medium. That saves time and money.

The problem is that E. coli does not naturally secrete every enzyme well. Protein folding and membrane transport can fail. The result is inclusion bodies, which are aggregated, inactive protein. Researchers need a signal peptide that directs the enzyme to the secretion pathway and keeps it soluble.

What the study did

The team used computer analysis to screen signal peptides for DPEase secretion in E. coli. They focused on localization and solubility. Signal peptide prediction identified PelB as the most effective candidate. PelB is a well-known signal peptide, but its performance depends on the passenger protein. Here, it worked.

The researchers then tested conditions that affect secretion. They added 0.1% Triton X-100, a nonionic detergent, to the culture. That treatment raised extracellular DPEase activity to 0.5 units per milliliter. They also expressed the enzyme at low temperature. Low-temperature expression reduced inclusion body formation, so more DPEase stayed in a soluble, active state.

Key findings

The evidence points to a simple combination. PelB gets the enzyme moving toward secretion. Triton X-100 helps release it from the cell. Low temperature keeps it folded correctly.

Strategy	Observed effect
PelB signal peptide	Best prediction for DPEase localization and solubility
0.1% Triton X-100	Extracellular DPEase activity reached 0.5 U/mL
Low-temperature expression	Reduced inclusion body formation

The 0.5 U/mL number matters. It tells you the process can deliver measurable extracellular activity, not just intracellular protein. That is the difference between a lab construct and a production candidate.

What it means for manufacturers

For enzyme suppliers, this is a low-cost process lever. PelB is not a new discovery. Triton X-100 is cheap. Cold expression adds some energy cost, but it can pay off through fewer inclusion bodies and easier recovery.

For allulose producers, the implication is downstream simplicity. If DPEase appears in the culture supernatant, you skip cell disruption. You also skip the cell debris that comes with lysis. That matters for food-grade enzyme preparation, because purification trains become shorter.

Ingredient buyers should watch for suppliers who use secretion-based DPEase. It often means better solubility and lower production cost, which can translate into price stability. Ask about the expression system. A supplier using PelB and permeabilization is likely running a more mature process.

FAQ

Does PelB work for every enzyme? No. Signal peptides are not universal. PelB performed best in this study for DPEase. You still need to test it with your own construct and strain.

Is 0.5 U/mL a high activity level? It depends on your process. The value matters because it is extracellular activity. For a secreted enzyme, 0.5 U/mL in the culture broth is a solid starting point for downstream concentration.

Can I use these conditions at scale? Triton X-100 is process-friendly in many fermentation settings. Low-temperature expression increases cooling load, but the reduction in inclusion bodies can offset that cost. Run a scale-down study first.

Closing

DPEase secretion in E. coli does not need a radical redesign. PelB, a mild detergent, and cooler growth conditions move the enzyme out of the cell and keep it active. For anyone building an allulose process, that is a small change with direct economic value.