A Novel D-Allulose 3-Epimerase from Staphylococcus aureus Redesigned for Improved Thermostability and Efficiency

If you are evaluating biocatalysts for D-allulose production, this paper gives you two specific mutants to watch. The researchers took a newly identified enzyme from Staphylococcus aureus and pushed it toward industrial relevance. Their work appears in Microbial Cell Factories under DOI 10.1186/s12934-019-1107-z.

Why this enzyme class matters

D-allulose is a rare sugar with nearly zero calories and a clean, sweet taste. Food formulators use it in beverage, bakery, and frozen dessert systems. But making D-allulose in bulk requires one critical step: converting D-fructose into D-allulose. That step depends on an enzyme called D-allulose 3-epimerase, or DAE.

Most DAEs work well in lab settings but fail under industrial conditions. They lose activity at high temperatures, slow down in concentrated sugar syrups, or die too quickly to reuse. Enzyme buyers need variants that survive process stress. The enzyme from Staphylococcus aureus — named SaDAE — offers a starting point. This study targeted that starting point with protein engineering.

What the study did

The team redesigned SaDAE using site-directed mutations. They wanted two things: higher catalytic productivity and better thermostability. They created a single mutant, V105A, and tested it for sugar conversion. They also built a triple mutant, S191D/M193E/S213C, specifically to see whether activity would hold at high temperatures.

The tests were direct. They used D-fructose as the substrate and measured how much D-allulose appeared at specific time points. They also incubated the triple mutant at 74.2°C and measured how much activity remained after 60 minutes.

Key evidence from the paper

The headline result is clear. SaDAE_V105A produced 190 g/L D-allulose from 500 g/L D-fructose in 6 hours. That is a conversion rate of 38.9%. For anyone running a fructose-to-allulose process, that yield is commercially meaningful.

The triple mutant tells a different but equally useful story. S191D/M193E/S213C lost only 50% of its activity after being incubated at 74.2°C for 60 minutes. That level of thermostability matters for enzyme immobilization and repeated batch runs.

Mutant	Conversion result	Thermostability result
SaDAE_V105A	190 g/L D-allulose from 500 g/L D-fructose in 6 h; 38.9% conversion	Not specified in evidence
S191D/M193E/S213C	Activity not specified in same conversion test	50% activity loss after 60 min at 74.2°C

Use these two mutants as benchmarks. One gives you high yield under moderate conditions. The other gives you a stability advantage when heat is unavoidable.

What it means for manufacturers

You can think about this paper in two ways.

First, the V105A mutant is a practical candidate for batch conversion. A 38.9% conversion in 6 hours is not the ceiling. It is a starting point for process optimization. With immobilized enzyme columns or fed-batch strategies, you may push that number higher. The key is that the enzyme is already operating on a high substrate load of 500 g/L D-fructose. That concentration is realistic, not lab fantasy.

Second, the triple mutant points to a path for reusability. Enzymes that hold activity at 74.2°C tolerate the exothermic conditions common in concentrated sugar syrups. They also survive longer on solid supports. That longer lifetime changes your unit cost per kilogram of D-allulose.

For ingredient buyers, this means supply risk may ease in the future. More stable enzymes allow producers to run longer campaigns, use less enzyme per batch, and keep product pricing predictable. That is the kind of technical progress you want to see before signing a supply agreement.

Frequently asked questions

Is D-allulose the same as D-psicose?
Yes. D-allulose is the accepted common name for D-psicose. The enzyme class may be called D-psicose 3-epimerase in older literature.

Why is thermostability such a big deal for enzyme suppliers?
Temperature stability allows you to run reactions at higher solids concentrations without losing enzyme activity. It also makes enzyme recycling practical. Both factors lower production costs.

Should I ask my supplier about these specific mutants?
You should ask whether their biocatalyst performs at 500 g/L fructose or higher. You can also ask about residual activity over multiple cycles. The specific mutation names are useful but less important than the performance data behind them.

The bottom line

This research gives the industry exactly what it lacks: more data on real enzymes under real process conditions. The V105A mutant delivers strong yield in a 6-hour window. The triple mutant shows what rational design can do for stability. Neither mutant is a finished commercial product, but both are reason to pay attention to SaDAE as a production platform.

Enzyme development moves slowly. Papers like this move it forward.