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

What this paper brings to the bench

If you buy or formulate enzymes for rare sugar production, the difference between a good enzyme and a mediocre one is not just activity. It’s how long that activity holds up under heat. This 2022 paper describes an optimized ultra-high-throughput screening assay for D-allulose 3-epimerase (DAEase) and uses it to create a variant that converts fructose to allulose better than the wild-type enzyme at 70°C.

Why DAEase is the bottleneck

D-allulose is the C-3 epimer of D-fructose. It tastes like sucrose and has similar sweetness, which makes it an attractive sugar replacer. To make allulose, you treat fructose with an epimerase enzyme. DAEase is the main workhorse for that reaction.

Industrial reactors run hot. Most wild-type epimerases lose activity too quickly under those conditions. Directed evolution can fix that, but only if you can screen enough mutants. Low-throughput assays slow the whole process and force researchers to test too few candidates.

How the screening assay was improved

The team optimized a PsiR-based ultra-high-throughput screening method specifically for DAEase directed evolution. That screening platform allowed them to sort large mutant libraries in less time. They first isolated a single mutant, I228V, which already showed improved specific activity and thermostability. Then they added two more substitutions to build the triple mutant I228V/D281G/C289R.

What the data showed

The triple mutant outperformed wild-type DAEase on the three metrics that matter most for production.

Metric	Wild type	I228V/D281G/C289R	Improvement
Specific activity	1.00 (reference)	1.42	42% higher
Half-life at 60°C	reference	extended	62.97-fold longer
Fructose-to-allulose conversion at 70°C	21.64%	28.11%	+6.47 percentage points

The specific activity gain is solid. The thermostability gain is the real standout. A 62.97-fold longer half-life at 60°C means the enzyme stays active far longer in a heated vessel. That matters in a commercial process where long hold times punish fragile proteins.

The conversion data are equally telling. At 70°C, the triple mutant converted 28.11% of D-fructose, compared with 21.64% for the wild-type enzyme. That is not a marginal bump. In a continuous process, that difference can reduce downstream purification load and raise overall yield.

What this means for allulose production

For formulators, the paper points to a practical enzyme profile: high activity plus high thermostability. You want an enzyme that can tolerate elevated temperatures and still convert substrate efficiently. This variant is a clear step in that direction.

For ingredient buyers, the bigger story is the screening platform itself. Ultra-high-throughput directed evolution is how enzyme suppliers discover variants like this in the first place. Faster screening means more sequence space covered, which means better commercial candidates down the line. If a supplier offers a DAEase with a similar mutation profile, this paper gives you a benchmark for asking about thermostability and conversion data.

Do not assume you can buy this exact variant today. The study is a research result, not a commercial product launch. Enzyme companies still need to scale up fermentation, formulate the enzyme for storage, and validate it in food-grade conditions. That said, for anyone sourcing allulose enzymes, the performance gap shown here is the kind of signal worth watching.

FAQs

Is the triple mutant ready for industrial use? Not yet. The data come from lab-scale experiments. Commercial use would require production-scale testing, formulation work, and regulatory review.

What does PsiR do in this assay? PsiR is the screening marker used in the optimized method. The authors built the assay around PsiR to make ultra-high-throughput screening feasible for DAEase directed evolution.

Does allulose production still start from fructose? Yes. DAEase converts D-fructose to D-allulose. The improved conversion at 70°C is exactly the kind of metric manufacturers look for when choosing an enzyme.

Enzyme engineering is a numbers game. This paper shows what happens when the screen gets faster and the target is set on real-world process conditions. The result is a variant that does more, at higher temperature, for longer. That is the direction the allulose industry needs to keep moving.