Generation of phytase chimeras with low sequence identities and improved thermal stability

Recent advances in phytase thermostability engineering towards potential application in the food and feed sectors

This review comprehensively examines the advancements in engineering thermostable phytase through genetic modification and immobilization techniques, focusing on developments from the last seven years. Genetic modifications, especially protein engineering, have enhanced enzyme's thermostability and functionality. Immobilization on various supports has further increased thermostability, with 50-60 % activity retention at higher temperature (more than 50 °C). In the food industry, phytase is used in flour processing and bread making, reducing phytate content by around 70 %, thereby improving nutritional value and mineral bioavailability. In the feed industry, it serves as a poultry feed additive, breaking down phytates to enhance nutrient availability and feed efficiency. The enzyme's robustness at high temperatures makes it valuable in feed processing. The integration of microbial production of phytase with genetically engineered strains followed by carrier free immobilization represents a synergistic approach to fortify enzyme structure and improve thermal stability. These advancement in the development of phytase enzyme capable of withstanding high temperatures, thereby pivotal for industrial utilization.

Food industry side streams: an unexploited source for biotechnological phosphorus upcycling

The phosphorus shortage is an unavoidable challenge that requires strategies to replace phosphorus sourced from ores. Food industry by-products are an unscoped resource for sustainable phosphorus recovery. Recent advances include biotechnological phosphorus upcycling from phytate-rich plant residues to polyphosphate as a food additive. The valorization of by-products such as deoiled seeds or brans additionally provides low-phosphorus feed and thereby minimizes the environmental burden. Phytate reduction in a cereal-rich diet by adding enzyme formulation is a further strategy that limits its antinutritive effect. However, sustainable P-management depends on phytases that have been customized and enhanced for thermostability and specific activity. The circular phosphorus economy is driven by emerging value chains and maturing phosphorus recovery technologies for market entry.

Engineering of the Phytase YiAPPA to Improve Thermostability and Activity and Its Application Potential in Dephytinization of Food Ingredients

The aim of this study was to modify phytase YiAPPA via protein surficial residue mutation to obtain phytase mutants with improved thermostability and activity, enhancing its application potential in the food industry. First, homology modeling of YiAPPA was performed. By adopting the strategy of protein surficial residue mutation, the lysine (Lys) and glycine (Gly) residues on the protein surface were selected for site-directed mutagenesis to construct single-site mutants. Thermostability screening was performed to obtain mutants (K189R and K216R) with significantly elevated thermostability. The combined mutant K189R/K216R was constructed via beneficial mutation site stacking and characterized. Compared with those of YiAPPA, the half-life of K189R/K216R at 80°C was extended from 14.81 min to 23.35 min, half-inactivation temperature (T50 30) was increased from 55.12°C to 62.44°C, and Tm value was increased from 48.36°C to 53.18°C. Meanwhile, the specific activity of K189R/K216R at 37°C and pH 4.5 increased from 3960.81 to 4469.13 U/mg. Molecular structure modeling analysis and molecular dynamics simulation showed that new hydrogen bonds were introduced into K189R/K216R, improving the stability of certain structural units of the phytase and its thermostability. The enhanced activity was primarily attributed to reduced enzyme-substrate binding energy and shorter nucleophilic attack distance between the catalytic residue His28 and the phytate substrate. Additionally, the K189R/K216R mutant increased the hydrolysis efficiency of phytate in food ingredients by 1.73-2.36 times. This study established an effective method for the molecular modification of phytase thermostability and activity, providing the food industry with an efficient phytase for hydrolyzing phytate in food ingredients.

Conditioning of Feed Material Prior to Feeding: Approaches for a Sustainable Phosphorus Utilization

A circular phosphorus (P) bioeconomy is not only worthwhile for conserving limited mineral P reservoirs, but also for minimizing negative environmental impacts caused by human-made alterations. Although P is an essential nutrient, most of the P in concentrates based on cereals, legumes and oilseed byproducts is organically bound to phytate. The latter cannot be efficiently utilized by monogastric animals and is therefore diluted into the environment through the manure pathway. This review examines various strategies for improved P utilization in animals and reflects the respective limitations. The strategies considered include feeding of debranned feedstuffs, pre-germinated feed, co-feeding of phytase and feeding material with high native phytase activity. All these approaches contribute to an improved P bioavailability. However, about half of the organic P content continues to be excreted and therefore remains unused by the animals. Nevertheless, technologies for an efficient utilization of P from cereal-based feed already exist; however, these are not industrially established. Conditioning feed material prior to feeding fosters P-reduced feed; meanwhile, P bound to phytate can be recovered. Based on known techniques for P separation and solubilisation from cereal products and phytate conversion, potential designs for feed material conditioning processes are proposed and evaluated.

Evolution of E. coli Phytase Toward Improved Hydrolysis of Inositol Tetraphosphate

Protein engineering campaigns are driven by the demand for superior enzyme performance under non-natural process conditions, such as elevated temperature or non-neutral pH, to achieve utmost efficiency and conserve limited resources. Phytases are industrial relevant feed enzymes that contribute to the overall phosphorus (P) management by catalyzing the stepwise phosphate hydrolysis from phytate, which is the main phosphorus storage in plants. Phosphorus is referred to as a critical disappearing nutrient, emphasizing the urgent need to implement strategies for a sustainable circular use and recovery of P from renewable resources. Engineered phytases already contribute today to an efficient phosphorus mobilization in the feeding industry and might pave the way to a circular P-bioeconomy. To date, a bottleneck in its application is the drastically reduced hydrolysis on lower phosphorylated reaction intermediates (lower inositol phosphates, ≤InsP4) and their subsequent accumulation. Here, we report the first KnowVolution campaign of the E. coli phytase toward improved hydrolysis on InsP4 and InsP3. As a prerequisite prior to evolution, a suitable screening setup was established and three isomers Ins(2,4,5)P3, Ins(2,3,4,5)P4 and Ins(1,2,5,6)P4 were generated through enzymatic hydrolysis of InsP6 and subsequent purification by HPLC. Screening of epPCR libraries identified clones with improved hydrolysis on Ins(1,2,5,6)P4 carrying substitutions involved in substrate binding and orientation. Saturation of seven positions and screening of, in total, 10,000 clones generated a dataset of 46 variants on their activity on all three isomers. This dataset was used for training, testing, and inferring models for machine learning guided recombination. The PyPEF method used allowed the prediction of recombinants from the identified substitutions, which were analyzed by reverse engineering to gain molecular understanding. Six variants with improved InsP4 hydrolysis of >2.5 were identified, of which variant T23L/K24S had a 3.7-fold improved relative activity on Ins(2,3,4,5)P4 and concomitantly shows a 2.7-fold improved hydrolysis of Ins(2,4,5)P3. Reported substitutions are the first published Ec phy variants with improved hydrolysis on InsP4 and InsP3.