Improving the performance of industrial ethanol-producing yeast by expressing the aspartyl protease on the cell surface

Advances in recombinant protease production: current state and perspectives

Proteases, enzymes that catalyze the hydrolysis of peptide bonds in proteins, are important in the food industry, biotechnology, and medical fields. With increasing demand for proteases, there is a growing emphasis on enhancing their expression and production through microbial systems. However, proteases' native hosts often fall short in high-level expression and compatibility with downstream applications. As a result, the recombinant production of proteases has become a significant focus, offering a solution to these challenges. This review presents an overview of the current state of protease production in prokaryotic and eukaryotic expression systems, highlighting key findings and trends. In prokaryotic systems, the Bacillus spp. is the predominant host for proteinase expression. Yeasts are commonly used in eukaryotic systems. Recent advancements in protease engineering over the past five years, including rational design and directed evolution, are also highlighted. By exploring the progress in both expression systems and engineering techniques, this review provides a detailed understanding of the current landscape of recombinant protease research and its prospects for future advancements.

Enhancing Geranylgeraniol Production by Metabolic Engineering and Utilization of Isoprenol as a Substrate in Saccharomyces cerevisiae

The amount of geranylgeranyl diphosphate (GGPP) is vital for microbial production of geranylgeraniol (GGOH) in Saccharomyces cerevisiae. In this study, a GGPP synthase with stronger catalytic ability was used to increase the supply of GGPP, and an engineered strain producing 374.02 mg/L GGOH at the shake flask level was constructed. Then, by increasing the metabolic flux of the mevalonate (MVA) pathway and the supply of isopentenyl pyrophosphate (IPP), the titer was further increased to 772.98 mg/L at the shake flask level, and we achieved the highest GGOH titer to date of 5.07 g/L in a 5 L bioreactor. This is the first report on the utilization of isoprenol for increasing the amount of IPP and enhancing GGOH production in S. cerevisiae. In the future, these strategies and engineered strains can be used to enhance the production of other terpenoids in S. cerevisiae.

Vps10-mediated targeting of Pep4 determines the activity of the vacuole in a substrate-dependent manner

The vacuole is the hydrolytic compartment of yeast cells and has a similar function as the lysosome of higher eukaryotes in detoxification and recycling of macromolecules. We analysed the contribution of single vacuolar enzymes to pexophagy and identified the phospholipase Atg15, the V-ATPase factor Vma2 and the serine-protease Prb1 along with the already known aspartyl-protease Pep4 (Proteinase A) to be required for this pathway. We also analysed the trafficking receptor Vps10, which is required for an efficient vacuolar targeting of the precursor form of Pep4. Here we demonstrate a novel context-dependent role of Vps10 in autophagy. We show that reduced maturation of Pep4 in a VPS10-deletion strain affects the proteolytic activity of the vacuole depending on the type and amount of substrate. The VPS10-deletion has no effect on the degradation of the cytosolic protein Pgk1 via bulk autophagy or on the degradation of ribosomes via ribophagy. In contrast, the degradation of an excess of peroxisomes via pexophagy as well as mitochondria via mitophagy was significantly hampered in a VPS10-deletion strain and correlated with a decreased maturation level of Pep4. The results show that Vps10-mediated targeting of Pep4 limits the proteolytic capacity of the vacuole in a substrate-dependent manner.

The Role of Microbial Aspartic Protease Enzyme in Food and Beverage Industries

Proteases represent one of the three largest groups of industrial enzymes and account for about 60% of the total global enzymes sale. According to the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology, proteases are classified in enzymes of class 3, the hydrolases, and the subclass 3.4, the peptide hydrolases or peptidase. Proteases are generally grouped into two main classes based on their site of action, that is, exopeptidases and endopeptidases. Protease has also been grouped into four classes based on their catalytic action: aspartic, cysteine, metallo, and serine proteases. However, lately, three new systems have been defined: the threonine-based proteasome system, the glutamate-glutamine system of eqolisin, and the serine-glutamate-aspartate system of sedolisin. Aspartic proteases (EC 3.4.23) are peptidases that display various activities and specificities. It has two aspartic acid residues (Asp32 and Asp215) within their active site which are useful for their catalytic activity. Most of the aspartic proteases display best enzyme activity at low pH (pH 3 to 4) and have isoelectric points in the pH range of 3 to 4.5. They are inhibited by pepstatin. The failure of the plant and animal proteases to meet the present global enzyme demand has directed to an increasing interest in microbial proteases. Microbial proteases are preferred over plant protease because they have most of the characteristics required for their biotechnological applications. Aspartic proteases are found in molds and yeasts but rarely in bacteria. Aspartic protease enzymes from microbial sources are mainly categorized into two groups: (i) the pepsin-like enzymes produced byAspergillus,Penicillium,Rhizopus, andNeurosporaand (ii) the rennin-like enzymes produced byEndothiaandMucorspp., such asMucor miehei,M. pusillus, andEndothia parasitica. Aspartic proteases of microbial origin have a wide range of application in food and beverage industries. These include as milk-clotting enzyme for cheese manufacturing, degradation of protein turbidity complex in fruit juices and alcoholic liquors, and modifying wheat gluten in bread by proteolysis.

Conventional process for ethanol production from Indian broken rice and pearl millet

A conventional process for ethanol production involving liquefaction followed by simultaneous saccharification and fermentation (SSF) under the yeast fermentation conditions, was investigated at 30 and 35% dry solid (DS) of Indian broken rice and pearl millet feedstocks. The study followed the typical conventional process currently in use by the Indian Ethanol Industry. Liquefaction was carried out using a thermostable alpha amylase, and whereas SSF with a glucoamylase with additional side activities of pullulanase and protease under the yeast fermentation conditions. To measure the enzyme efficacy in the liquefaction process, fermentable sugar and liquefact solubility (brix) were monitored at the end of the liquefaction process. The liquefact was subjected to SSF with yeast. Addition of an acid fungal protease at a concentration of 0.1 kg per metric ton of grain during SSF was observed to accelerate yeast growth and ultimately, ethanol yield with both feedstocks. With both concentrations of feedstocks, the fermentation efficiency and ethanol recovery were determined. This study assesses the potential of these enzymes for ethanol production with higher dry solid concentration (≥30% w/w DS) of both these feedstocks in the conventional process to achieve higher plant throughput without compromising fermentation efficiency and ethanol recovery.