A Growth-Coupled Epimerase Evolution Platform Using Biosen Improves D-Allulose Biosynthesis

The enzyme bottleneck in D-allulose production

D-Allulose comes from D-fructose, and the conversion depends on ketose 3-epimerases (KEases). These enzymes work, but they don’t always work well enough. Natural versions often show weak catalytic activity and limited heat tolerance. For an ingredient that competes on cost, that’s a problem. Faster enzymes mean lower production cost. Stable enzymes mean longer reaction times and better enzyme reuse. So enzyme engineers keep looking for better mutants.

The paper, published in Advanced Science (DOI: 10.1002/advs.202306478), tackles this directly.

Why screening slows enzyme evolution

Directed evolution can create better KEases. The bottleneck is screening. Traditional methods test each mutant one by one in microtiter plates. That is slow. It is also expensive. Many labs avoid it because the effort is so high.

This study removes that bottleneck in a clever way. Instead of measuring D-allulose, the researchers made cells depend on it.

What the study did

The team built a D-allulose-dependent biosensor called Biosen. The sensor connects D-allulose levels to cell growth. When an enzyme makes D-allulose, the sensor switches on and cells grow. Better enzymes make more allulose, so those cells grow faster. That creates a growth-coupled selection pressure.

The group applied this pressure to ADAE, a ketose 3-epimerase. They evolved new variants without picking and measuring every clone. Only cells that produced enough D-allulose survived and multiplied. That is a fundamentally different screening logic.

Key findings

One mutant, M42, stood out. Its catalytic activity increased 6.28-fold compared with the wild-type enzyme. Its half-life at 60°C extended 2.5-fold. In a 3-hour reaction, it converted D-fructose to D-allulose at a 32.2% yield.

Those numbers matter. The activity jump reduces enzyme loading. The heat tolerance opens more process options. And the conversion level fits with what manufacturers would need before downstream purification.

Screening method	Selection pressure	Practical result
Traditional microtiter plate	None; manual picking	Labor-heavy, limited by human effort
Biosen growth-coupled screen	Strong; growth depends on allulose production	M42: 6.28x activity, 2.5x stability, 32.2% yield

What this means for manufacturers

Formulators and ingredient buyers should watch this. The method is not just about one mutant. It gives enzyme suppliers a high-throughput tool to customize KEases for specific process conditions.

Ask suppliers how they evolved their enzymes. If they used growth-coupled selection, the enzyme may already be more process-relevant. For D-allulose production, the immediate benefit is a biocatalyst that works under heat and produces more product in the same reactor.

One caveat: M42 is still a lab result. Scaling to pilot or commercial production takes more work. But the screening direction is clear.

Frequently asked questions

What exactly is growth-coupled screening?

It couples a desired output to cell survival. Here, D-allulose triggers a biosensor that drives growth. Only mutants that make enough allulose grow fast. That gives you selection instead of manual picks.

Does this mean M42 is ready for commercial production?

Not yet. It is a research result, not an industrial enzyme. But it shows the platform can deliver a mutant with stronger activity and better heat tolerance, which are exactly the traits formulators care about.

Can this method apply to other sugars?

The concept should transfer to any sugar where you can build a biosensor. The team targeted D-allulose, but the screening logic is general.

The allulose market runs on process economics. Enzymes sit at the heart of that cost. If growth-coupled screening becomes standard, we may see more mutants that survive real-world conditions. That is the kind of progress formulators can use.