Biosensor-Driven Growth-Coupled Evolution of Epimerase Improves D-Allulose Biosynthesis

The enzyme problem in allulose production

D-allulose tastes like sugar, but making it at scale is an enzyme challenge. The best conversion route flips D-fructose into D-allulose using ketose 3-epimerases (KEases). Those enzymes are often too slow or too fragile. Heat destroys them. That pushes up cost.

A new paper in Advanced Science (DOI: 10.1002/advs.202306478) tackles exactly this. Researchers built a growth-coupled in vivo screening platform that links D-allulose production to bacterial survival. They used it to evolve KEases under real selection pressure. The result: a mutant with significantly better activity and thermostability.

Why enzyme screening usually fails

Most directed evolution screens are laborious. You mutate, pick colonies, assay each one. That works, but it limits how many variants you can test. It also misses rare hits.

The group behind this paper wanted a faster, smarter approach. Their answer uses a D-allulose-dependent biosensor. When a cell makes D-allulose, the biosensor triggers a growth signal. Cells with better enzymes grow better. That is the “growth-coupled” part. No one has to manually measure every variant. The culture does the selection for you.

The Chinese title of the paper mentions Biosen, which fits the biosensor-driven strategy. The platform is in vivo, meaning evolution happens inside living cells.

What the study did

The researchers engineered ketose 3-epimerases (KEases) using this biosensor platform. They applied evolutionary pressure to create variants with improved performance. Then they characterized the best one, an ADAE mutant called M42.

M42’s numbers stand out:

• Catalytic activity: 6.28 times higher than the parent enzyme
• Half-life at 60°C: 2.5 times longer
• Conversion of D-fructose to D-allulose: 32.2% in 3 hours

That conversion number matters for formulators. A 32.2% yield after three hours is a practical benchmark. It means the enzyme can do substantial work quickly, before heat or substrate side reactions get in the way.

Here is a simple view of the reported performance:

Metric	M42 mutant vs parent
Catalytic activity	6.28× higher
Half-life at 60°C	2.5× longer
D-fructose → D-allulose conversion (3 h)	32.2%

What this means for ingredient buyers

D-allulose pricing depends on enzyme cost. Slow enzymes require more enzyme loading, longer holding times, and bigger reactors. Fragile enzymes demand cold-chain handling or frequent replacement. A more active, more heat-stable KEase directly lowers those costs.

For a formulator, the short reaction time is also attractive. A 3-hour conversion window fits batch processing schedules. It allows glucose isomerase or downstream refining steps to move forward without a long wait. And the improved thermostability means less enzyme denaturation at the 60°C range where isomerization reactions often run.

The screening method itself could become the bigger story. If growth-coupled biosensor screening works this well for KEases, the same platform can be adapted to other sugar epimerases and isomerases. That could accelerate the whole sweetener enzyme pipeline.

FAQ

What does growth-coupled screening mean? It links the desired enzyme activity to cell growth. Cells with active D-allulose-forming enzymes trigger a biosensor, which makes them grow faster. Over multiple rounds, the population becomes enriched with better enzyme variants.

Is M42 ready for commercial production? The paper does not report pilot-scale or food-grade validation. It shows a strong enzyme variant and a useful screening tool. Manufacturers would still need process development and regulatory review before commercial use.

Why does thermostability matter in allulose production? Fructose isomerization often runs at elevated temperatures to improve solubility and reaction rate. An enzyme with a longer half-life at 60°C can sustain that rate for more batches. That cuts enzyme cost per kilogram of allulose.

A better enzyme is only the start

The biosensor approach changes how quickly enzyme candidates can be found. M42 is the proof, with a six-fold activity gain and a 2.5-fold thermostability gain. The next steps belong to process engineers. They will test M42 in realistic substrate syrups, optimize enzyme loading, and determine whether the 32.2% conversion holds outside the lab. For buyers, the direction is clear: biosensor-driven evolution is bringing better allulose enzymes closer to market.