Optimization of an Ultra-High-Throughput Screening Assay for Protein Engineering of D-Allulose 3-Epimerase

Allulose formulators face a common problem: the enzymes that make allulose don’t always hold up at industrial temperatures. This paper from Biomolecules describes a faster way to find better ones. The method works. It yielded a variant with 1.42 times the specific activity of wild-type enzyme and a 62.97-fold longer half-life at 60°C.

Allulose needs better enzymes

D-allulose is the C-3 epimer of D-fructose. It tastes similar to sucrose, but with fewer calories. To produce it, manufacturers use D-allulose 3-epimerase (DAEase) to convert fructose into allulose. The reaction works, but naturally occurring DAEase is not optimized for heat and long reaction times. You can push temperature higher to speed conversion, but the enzyme denatures. You can run longer, but productivity drops. The industry needs enzyme variants with both high activity and thermostability.

How the screening bottleneck got addressed

Directed evolution can create those variants, but screening thousands of mutants is tedious. The researchers optimized a PsiR-based ultra-high-throughput screening method for DAEase directed evolution. That gave them a starting mutant, I228V, from the first round. Then they stacked additional mutations on top. The result was a triple mutant: I228V/D281G/C289R.

This isn’t just a lab curiosity. The triple mutant’s performance was measured under conditions close to industrial use.

What the data show

The numbers matter for scale-up. The triple mutant’s specific activity jumped to 1.42 times the wild-type level. At 60°C, its half-life increased by 62.97 times. In a biosynthesis test at 70°C, the triple mutant converted 28.11% of D-fructose to D-allulose, versus 21.64% for wild-type.

Metric	Wild-type DAEase	Triple mutant I228V/D281G/C289R
Relative specific activity	1.0	1.42
Half-life at 60°C	Baseline	62.97x longer
Conversion at 70°C	21.64%	28.11%

That 6.47 percentage-point gain may not sound huge, but at commercial scale it changes downstream costs. Higher conversion means less leftover fructose in the syrup. That means easier separation, less chromatography load, and lower operating expenses.

What this means for formulators and buyers

For product developers, the practical takeaway is that enzyme suppliers now have a clear path to better DAEase variants. An enzyme with a 62.97-fold longer half-life at 60°C allows longer reaction cycles without adding fresh enzyme. It also opens the door to running at 70°C, which improves reaction rate and reduces the risk of microbial contamination.

For ingredient buyers, this paper is a reason to ask suppliers how they screen their enzymes. Not all DAEases are equal. Ask for thermostability data, not just initial activity. A variant like I228V/D281G/C289R could cut enzyme usage or increase plant throughput. That affects the final cost per kilo of allulose.

The research also validates the screening approach. PsiR-based ultra-high-throughput screening can handle large libraries. That means future improvements—better specificity, different pH tolerance, higher conversion—can be found faster. For a commodity sweetener, those incremental gains add up.

FAQ

What is DAEase? DAEase stands for D-allulose 3-epimerase. It’s the enzyme that converts D-fructose into D-allulose.

Is the triple mutant ready for commercial production? The paper reports lab-scale biosynthesis at 70°C. It doesn’t describe full industrial validation. You’d want pilot testing in your own process.

Does the PsiR-based screening method require special equipment? The paper doesn’t detail equipment requirements. But ultra-high-throughput screening typically works with fluorescence-activated cell sorting or similar platforms.

The takeaway is simple. Better screening leads to better enzymes. And better enzymes make allulose production more economical. This paper shows exactly how much improvement is possible: 1.42 times the specific activity, 62.97 times the half-life, and a conversion rate that beats wild-type by six full points. Ask your enzyme partner if they’re using tools like this. If not, it may be time to switch.