Preparation of (S)-epichlorohydrin using a novel halohydrin dehalogenase by selective conformation adjustment.

Chiral epichlorohydrin (ECH) is an attractive intermediate for chiral pharmaceuticals and chemicals preparation. The asymmetric synthesis of chiral ECH using 1,3-dicholoro-2-propanol (1,3-DCP) catalyzed by a haloalcohol dehalogenase (HHDH) was considered as a feasible approach. However, the reverse ring opening reaction caused low optical purity of chiral ECH, thus severely restricts the industrial application of HHDHs. In the present study, a novel selective conformation adjustment strategy was developed with an engineered HheCPS to regulate the kinetic parameters of the forward and reverse reactions, based on site saturation mutation and molecular simulation analysis. The HheCPS mutant E85P was constructed with a markable change in the conformation of (S)-ECH in the substrate pocket and a slight impact on the interaction between 1,3-DCP and the enzyme, which resulted in the kinetic deceleration of the reverse reactions. Compared with HheCPS, the catalytic efficiency (kcat(S)-ECH/Km(S)-ECH) of the reversed reaction dropped to 0.23-fold (from 0.13 to 0.03 mM-1 s-1), while the catalytic efficiency (kcat(1,3-DCP)/Km(1,3-DCP)) of the forward reaction only reduced from 0.83 to 0.71 mM-1 s-1. With 40 mM 1,3-DCP as substrate, HheCPS E85P catalyzed the synthesis of (S)-ECH with the yield up to 55.35% and the e.e. increased from 92.54 to >99%. Our work provided an effective approach for understanding the stereoselective catalytic mechanism as well as the green manufacturing of chiral epoxides.

Effects of cluster nursing interventions on the prevention of pressure ulcers in intensive care units patients: A meta-analysis.

A meta-analysis was conducted to comprehensively evaluate the impact of cluster nursing interventions on the prevention of pressure ulcers (PUs) in intensive care unit (ICU) patients. Computer searches were performed in databases including Embase, Google Scholar, Cochrane Library, PubMed, Wanfang and China National Knowledge Infrastructure for randomized controlled trials (RCTs) implementing cluster nursing interventions for PUs prevention in ICU patients, with the search period covering the database inception to November 2023. Two researchers independently screened the literature, extracted data and conducted quality assessments. Stata 17.0 software was employed for data analysis. Overall, 17 RCTs involving 1463 ICU patients were included. The analysis showed that compared with conventional nursing, cluster nursing interventions significantly reduced the incidence of PUs (odds ratio: 0.24, 95% confidence intervals [CI]: 0.17-0.34, p < 0.001) and also significantly improved the levels of anxiety (standardized mean difference [SMD]: -1.39, 95% CI: -1.57 to 1.22, p < 0.001) and depression (SMD: -1.64, 95% CI: -2.02 to 1.26, p < 0.001) in ICU patients. This study indicates that the application of cluster nursing interventions in ICU patients can effectively reduce the incidence of PUs, as well as improve patients' anxiety and depression levels, thereby enhancing their quality of life, which is worth clinical promotion and application.

Rational Regulation of Reaction Specificity of Nitrilase for Efficient Biosynthesis of 2-Chloronicotinic Acid through a Single Site Mutation.

Nitrilase-catalyzed hydrolysis of 2-chloronicotinonitrile (2-CN) is a promising approach for the efficient synthesis of 2-chloronicotinic acid (2-CA). The development of nitrilase with ideal catalytic properties is crucial for the biosynthetic route with industrial potential. Herein, a nitrilase from Rhodococcus zopfii (RzNIT), which showed much higher hydration activity than hydrolysis activity, was designed for efficient hydrolysis of 2-CN. Two residues (N165 and W167) significantly affecting the reaction specificity were precisely identified. By tuning these two residues, a single mutation of W167G with abolished hydration activity and 20-fold improved hydrolysis activity was obtained. Molecular dynamics simulation and molecular docking revealed that the mutation generated a larger binding pocket, causing the substrate 2-CN to bind more deeply in the pocket and form a delocalized π bond between the residues W190 and Y196, which reduced the negative influence of steric hindrance and electron effect caused by chlorine substituent. With mutant W167G as biocatalyst, 100 mM 2-CN was exclusively converted into 2-CA within 16 h. The study provides useful guidance in nitrilase engineering for simultaneous improvement of reaction specificity and catalytic activity, which are highly desirable in value-added carboxylic acids production from nitriles hydrolysis. IMPORTANCE 2-CA is an important building block for agrochemicals and pharmaceuticals with a rapid increase in demand in recent years. It is currently manufactured from 3-cyanopyridine by chemical methods. However, during the final step of 2-CN hydrolysis under high temperature and strong alkaline conditions, the byproduct 2-CM was generated except for the target product, leading to low yield and tedious separation steps. Nitrilase-mediated hydrolysis is regarded as a promising alternative for 2-CA production, which proceeded under mild conditions. Nevertheless, nitrilase capable of efficient hydrolysis of 2-CN has not been reported because the enzymes showed either extremely low activity or surprisingly high hydration activity toward 2-CN. Herein, the reaction specificity of RzNIT was precisely tuned through a single site mutation. The mutant exhibited remarkably enhanced hydrolysis activity without the formation of byproducts, providing a robust biocatalyst for 2-CA biosynthesis with industrial potential.

High-throughput assay of tyrosine phenol-lyase activity using a cascade of enzymatic reactions.

Tyrosine phenol-lyase (TPL) exhibits great potential in industrial biosynthesis of l-tyrosine and its derivates. To uncover and screen TPLs with excellent catalytic properties, there is unmet demand for development of facile and reliable screening system for TPL. Here we presented a novel assay format for the detection of TPL activity based on catechol 2,3-dioxygenase (C23O)-catalyzed reaction. Catechol released from TPL-catalyzed cleavage of 3,4-dihydroxy-l-phenylalanine (l-DOPA) was further oxidized by C23O to form 2-hydroxymuconate semialdehyde, which could be readily detected by spectrophotometric measurements at 375 nm. The assay achieved a unique balance between the ease of operation and superiority of analytical performances including linearity, sensitivity and accuracy. In addition, this assay enabled real-time monitoring of TPL activity with high efficiency and reliability. As C23O is highly specific towards catechol, a non-natural product of microorganism, the assay was therefore accessible to both crude cell extracts and the whole-cell system without elaborate purification steps of enzymes, which could greatly expedite discovery and engineering of TPLs. This study provided fundamental principle for high-throughput screening of other enzymes consuming or producing catechol derivatives.

Improvement of multicatalytic properties of nitrilase from Paraburkholderia graminis for efficient biosynthesis of 2-chloronicotinic acid.

Nitrilases are promising biocatalysts to produce high-value-added carboxylic acids through hydrolysis of nitriles. However, since the enzymes always show low activity and sometimes with poor reaction specificity toward 2-chloronicotinonitrile (2-CN), very few robust nitrilases have been reported for efficient production of 2-chloronicotinic acid (2-CA) from 2-CN. Herein, a nitrilase from Paraburkholderia graminis (PgNIT) was engineered to improve its catalytic properties. We identified the beneficial residues via computational analysis and constructed the mutant library. The positive mutants were obtained and the activity of the "best" mutant F164G/I130L/N167Y/A55S/Q260C/T133I/R199Q toward 2-CN was increased from 0.14 × 10-3  to 4.22 U/mg. Its reaction specificity was improved with elimination of hydration activity. Molecular docking and molecular dynamics simulation revealed that the conformational flexibility, the nucleophilic attack distance, as well as the interaction forces between the enzyme and substrate were the main reason alternating the catalytic properties of PgNIT. With the best mutant as biocatalyst, 150 g/L 2-CN was completely converted, resulting in 2-CA accumulated to 169.7 g/L. When the substrate concentration was increased to 200 g/L, 203.1 g/L 2-CA was obtained with yield of 85.7%. The results laid the foundation for industrial production of 2-CA with the nitrilase-catalyzed route.

Regulating substrate preference of phosphatase by reshaping the "cap domain" for multi-enzymatic biosynthesis of high-purity monosaccharides.

Phosphatases are a class of enzymes catalyzing the cleavage of monophosphate ester bonds from the phosphorylated substrates. They have important applications in construction of in vitro multi-enzymatic system for monosaccharides. However, the enzymes generally show substrate ambiguity, which has become a bottleneck for efficient biosynthesis of target products with high purity. In this study, semirational design was performed on phosphatase from Thermosipho atlanticus (Ta-PST). The hotspot amino acid residues forming a "cap domain" were identified and selected for saturation mutagenesis. The mutant F179T and F179M showed improved substrate preference toward fructose-6-phosphate and mannose-6-phosphate, respectively. Coupling with other enzymes involved in the multi-enzymatic system under optimized conditions, the application of F179T led to fructose yield of 80% from 10 g/L maltodextrin and the ratio between the target product and by-product glucose was increased from 2:1 to 19:1. On the other hand, the application of F179M led to mannose yield of 59% with ratio of mannose to the by-products glucose and fructose increased from 1:1:1 to 14:2:1. Moreover, the molecular understanding of the beneficial substitution was gained by structural analysis and molecular dynamic simulations, giving important guidance to regulate the enzyme's substrate preference.

Efficient strategies to enhance plasmid stability for fermentation of recombinant Escherichia coli harboring tyrosine phenol lyase.

OBJECTIVE: To solve the bottleneck of plasmid instability during microbial fermentation of L-DOPA with recombinant Escherichia coli expressing heterologous tyrosine phenol lyase. RESULTS: The tyrosine phenol lyase from Fusobacterium nucleatum was constitutively expressed in E. coli and a fed-batch fermentation process with temperature down-shift cultivation was performed. Efficient strategies including replacing the original ampicillin resistance gene, as well as inserting cer site that is active for resolving plasmid multimers were applied. As a result, the plasmid stability was increased. The co-use of cer site on plasmid and kanamycin in culture medium resulted in proportion of plasmid containing cells maintained at 100% after fermentation for 35 h. The specific activity of tyrosine phenol lyase reached 1493 U/g dcw, while the volumetric activity increased from 2943 to 14,408 U/L for L-DOPA biosynthesis. CONCLUSIONS: The established strategies for plasmid stability is not only promoted the applicability of the recombinant cells for L-DOPA production, but also provides important guidance for industrial fermentation with improved microbial productivity.

Recent advancements in enzyme engineering via site-specific incorporation of unnatural amino acids.

With increased attention to excellent biocatalysts, evolving methods based on nature or unnatural amino acid (UAAs) mutagenesis have become an important part of enzyme engineering. The emergence of powerful method through expanding the genetic code allows to incorporate UAAs with unique chemical functionalities into proteins, endowing proteins with more structural and functional features. To date, over 200 diverse UAAs have been incorporated site-specifically into proteins via this methodology and many of them have been widely exploited in the field of enzyme engineering, making this genetic code expansion approach possible to be a promising tool for modulating the properties of enzymes. In this context, we focus on how this robust method to specifically incorporate UAAs into proteins and summarize their applications in enzyme engineering for tuning and expanding the functional properties of enzymes. Meanwhile, we aim to discuss how the benefits can be achieved by using the genetically encoded UAAs. We hope that this method will become an integral part of the field of enzyme engineering in the future.

Development of a robust nitrilase by fragment swapping and semi-rational design for efficient biosynthesis of pregabalin precursor.

Protein engineering is a powerful tool for improving the properties of enzymes. However, large changes in enzyme properties are still challenging for traditional evolution strategies because they usually require multiple amino acid substitutions. In this study, a feasible evolution approach by a combination of fragment swapping and semi-rational design was developed for the engineering of nitrilase. A chimera BaNIT harboring 12 amino acid substitutions was obtained using nitrilase from Arabis alpine (AaNIT) and Brassica rapa (BrNIT) as parent enzymes, which exhibited higher enantioselectivity and activity toward isobutylsuccinonitrile for the biosynthesis of pregabalin precursor. The semi-rational design was executed on BaNIT to further generate variant BaNIT/L223Q/H263D/Q279E with the concurrent improvement of activity, enantioselectivity, and solubility. The robust nitrilase displayed a 5.4-fold increase in whole-cell activity and the enantiomeric ratio (E) increased from 180 to higher than 300. Molecular dynamics simulation and molecular docking demonstrated that the substitution of residues on the A and C surface contributed to the conformation alteration of nitrilase, leading to the simultaneous enhancement of enzyme properties. The results obtained not only successfully engineered the nitrilase with great industrial potential for the production of pregabalin precursor, but also provided a new perspective for the development of novel industrially important enzymes.

Enhanced production of L-methionine in engineered Escherichia coli with efficient supply of one carbon unit.

OBJECTIVE: L-methionine is an important sulfur-containing amino acid essential for humans and animals. Its biosynthesis pathway is complex and highly regulated. This study aims to explore the bottleneck limiting the improvement of L-methionine productivity and apply efficient strategies to increase L-methionine production in engineered E. coli. RESULTS: The enzyme O-succinylhomoserine sulfhydrylase involved in thiolation of OSH to form homocysteine was overexpressed in the engineered strain E. coli W3110 IJAHFEBC/PAm, resulting in L-methionine production increased from 2.8 to 3.22 g/L in shake flask cultivation. By exogenous addition of L-glycine as the precursor of one carbon unit, the titer of L-methionine was increased to 3.68 g/L. The glycine cleavage system was further strengthened for the efficient one carbon unit supply and a L-methionine titer of 3.96 g/L was obtained, which was increased by 42% compared with that of the original strain. CONCLUSIONS: Insufficient supply of one carbon unit was found to be the issue limiting the improvement of L-methionine productivity and its up-regulation significantly promoted the L-methionine production in the engineered E. coli.

Structure-Based Engineering of Amidase from Pantoea sp. for Efficient 2-Chloronicotinic Acid Biosynthesis.

2-Chloronicotinic acid is a key intermediate of pharmaceuticals and pesticides. Amidase-catalyzed hydrolysis provides a promising enzymatic method for 2-chloronicotinic acid production from 2-chloronicotinamide. However, biocatalytic hydrolysis of 2-chloronicotinamide is difficult due to the strong steric and electronic effect caused by 2-position chlorine substituent of the pyridine ring. In this study, an amidase from a Pantoea sp. (Pa-Ami) was designed and engineered to have improved catalytic properties. Single mutant G175A and double mutant G175A/A305T strains exhibited 3.2- and 3.7-fold improvements in their specific activity for 2-chloronicotinamide, and the catalytic efficiency was significantly increased, with kcat/Km values 3.1 and 10.0 times higher than that of the wild type, respectively. Structure-function analysis revealed that the distance between Oγ of Ser177 (involved in the catalytic triad) and the carbonyl carbon of 2-chloronicotinamide was shortened in the G175A mutant, making the nucleophilic attack on the Oγ of Ser177 easier by virtue of proper orientation. In addition, the A305T mutation contributed to a suitable tunnel formation to facilitate the substrate entry and product release, resulting in improved catalytic efficiency. With the G175A/A305T double mutant as a biocatalyst, a maximum of 1,220 mM 2-chloronicotinic acid was produced with a 94% conversion, and the space-time yield reached as high as 575 gproduct liter-1 day-1 These results provide not only a novel robust biocatalyst for the production of 2-chloronicotinic acid but also new insights into amidase structure-function relationships.IMPORTANCE In recent years, the demand for 2-chloronicotinic acid has been greatly increased. To date, several chemical methods have been used for the synthesis of 2-chloronicotinic acid, but all include tedious steps and/or drastic reaction conditions, resulting in both economic and environmental issues. It is requisite to develop an efficient and green synthesis route. We recently screened Pa-Ami and demonstrated its potential for synthesis of 2-chloronicotinic acid from 2-chloronicotinamide. However, chlorine substitution on the pyridine ring of nicotinamide significantly affected the activity of Pa-Ami. Especially for 2-chloronicotinamide, the enzyme activity and catalytic efficiency were relatively low. In this study, based on structure-function analysis, we succeeded in engineering the amidase by structure-guided saturation mutagenesis. The engineered Pa-Ami exhibited quite high catalytic activity toward 2-chloronicotinamide and could serve as a promising biocatalyst for the biosynthesis of 2-chloronicotinic acid.

Highly regio- and enantioselective synthesis of chiral intermediate for pregabalin using one-pot bienzymatic cascade of nitrilase and amidase.

Nitrilase-mediated hydrolysis of isobutylsuccinonitrile (IBSN) is a highly attractive approach for (S)-3-cyano-5-methylhexanoic acid ((S)-CMHA), the critical chiral intermediate of pregabalin. In this study, a robust nitrilase from Arabis alpina (AaNIT) was screened and engineered. The N258D mutant was obtained with high catalytic activity and excellent enantioselectivity (E > 300) towards IBSN at a high substrate concentration of 100 g L-1. Byproduct (S)-3-cyano-5-methyl hexanoic amide ((S)-CMHM) was detected and identified for the first time during the catalytic process. By employing a feasible one-pot bienzymatic cascade of mutant N258D and amidase from Pantoea sp. (Pa-Ami) expressed separately in recombinant Escherichia coli cells, the byproduct (S)-CMHM was eliminated and (S)-CMHA was obtained with a conversion of 45.0% and eep of 99.3%. These results provided the novel plant-derived nitrilase as a promising biocatalyst for (S)-CMHA biosynthesis and demonstrated the feasibility of one-pot bienzymatic cascade reaction for large-scale production of the pregabalin precursor.

Identification and engineering of the key residues at the crevice-like binding site of lipases responsible for activity and substrate specificity.

OBJECTIVE: Rational engineering of the crevice-like binding site of lipases for improvement of lipases' catalytic properties. RESUTS: The residues located at the crevice-like binding site of four representative lipases including Thermomyces lanuginosus lipases (TLL and Lip), Rhizopus oryzae lipase (ROL), and Rhizomucor miehei lipase (RML) were identified through structural analysis. The residues at the bottom of the crevice-like binding site recognizing the substrates with short/medium carbon chain length and those located at the right-hand wall of the surface crevice region affecting the product release were changed by site-directed mutagenesis. The corresponding double mutants exhibited ~ 5 to 14-fold higher activity towards p-nitrophenyl esters than their wild types, and their substrate preference shifted to acyl moiety with shorter carbon chain length. In addition, the mutations led to an increase of B-factor, resulting in decrease of their optimum temperature by 10-20 °C. CONCLUSIONS: The key residues located at the crevice-like binding site play important roles in determining lipase activity, substrate preference and optimum temperature, which offers a useful new paradigm for facilitating rational design of lipases.

Statistical medium optimization and DO-STAT fed-batch fermentation for enhanced production of tyrosine phenol lyase in recombinant Escherichia coli.

Tyrosine phenol lyase (TPL) is a robust biocatalyst for the production of L-dihydroxyphenylalanine (L-DOPA). The improvement of TPL production is conducive to the industrial potential. In this study, the optimization of culture medium of recombinant Escherichia coli harboring TPL from Fusobacterium nucleatum (Fn-TPL) was carried out. Sucrose and combination of yeast extract and peptone were selected as carbon and nitrogen source, respectively. Their optimal concentrations were determined by Box-Behnken design and the synergistic effect between yeast extract and peptone was found to be significant, with p-value < 0.05. The DO-STAT fed-batch fermentation under optimized culture condition was established and the oxygen level was fixed at 20%. Both the biomass and Fn-TPL activity were significantly increased, which were 35.6 g dcw/L and 12292 U/L, respectively. The results obtained significantly promote the industrial production of L-DOPA production.

An efficient colorimetric high-throughput screening method for synthetic activity of tyrosine phenol-lyase.

Tyrosine phenol-lyase (TPL) naturally catalyzes the reversible ß-elimination of l-tyrosine to phenol, pyruvate and ammonium. With its reverse reaction (synthetic activity), l-tyrosine and its derivatives could be synthesized with high atom economy, which are widely used in pharmaceutical industries. In this study, a high-throughput screening method for synthetic activity of TPL was developed. One of the substrate, sodium pyruvate was found to react with salicylaldehyde under alkali condition, forming a yellow color compound. The concentration of sodium pyruvate can be quantified according to the absorbance of the colorimetric compound at wavelength of 465 nm and the activity of TPL could be screened according to the decrease of the absorbance. After optimization of the colorimetric reaction conditions, the established high-throughput screening method was successfully used for screening of TPL with enhanced activity for l-DOPA synthesis. The confirmed sensitivity and accuracy demonstrated the feasibility and application potential of this screening method.

Engineering of Talaromyces thermophilus lipase by altering its crevice-like binding site for highly efficient biocatalytic synthesis of chiral intermediate of Pregablin.

The scissile fatty acid binding site of lipases is divided into different sub-groups and plays an important role in the catalytic properties of the enzymes. In this study, the Talaromyces thermophilus lipase was engineered by altering its crevice-like binding site for efficient synthesis of chiral intermediate of Pregablin through kinetic resolution of 2-carboxyethyl-3-cyano-5-methylhexanoic acid ethyl ester (CNDE). The substitution of residues located at the crevice-like binding site with phenylalanine (Phe) resulted in significantly increased hydrolysis activity. The variant L206F/P207F/L259F exhibited a 37.23-fold and 47.02-fold improvement in the specific activity and turnover number (kcat) toward CNDE, respectively. Simultaneously, the optimum temperature and substrate preference were both altered in the variants. The study herein successfully engineered the TTL with improved catalytic properties for efficient biosynthesis of Pregablin intermediate. The investigation of structure-functional relationship provided important guidance for further modification of lipases with crevice-like binding site domain.

Efficient chemoenzymatic synthesis of (S)-α-amino-4-fluorobenzeneacetic acid using immobilized penicillin amidase.

An efficient chemoenzymatic route was developed for synthesis of (S)-α-amino-4-fluorobenzeneacetic acid, a valuable chiral intermediate of Aprepitant, using immobilized penicillin amidase catalyzed kinetic resolution of racemic N-phenylacetyl-4-fluorophenylglycine. The optimum temperature, pH and agitation rate of the reaction were determined to be 40 °C, 9.5 and 300 rpm, respectively. Kinetic resolution of 80 g L-1N-phenylacetyl-4-fluorophenylglycine by immobilized amidase 20 g L-1 resulted in 49.9% conversion and >99.9% e.e. within 3 h. The unreacted N-phenylacetyl-4-fluorophenylglycine can be easily racemized and then recycled as substrate. The production of (S)-α-amino-4-fluorobenzeneacetic acid was further amplified in 1 L reaction system, affording excellent conversion (49.9%) and enantioselectivity (99.9%). This chemoenzymatic approach was demonstrated to be promising for industrial production of (S)-α-amino-4-fluorobenzeneacetic acid.

Biocatalytic hydrolysis of chlorinated nicotinamides by a superior AS family amidase and its application in enzymatic production of 2-chloronicotinic acid.

2-Chloronicotinic acid (2-CA) is an important building block for a series of agrochemicals and pharmaceuticals. Amidase-catalyzed hydrolysis of 2-chloronicotinamide is one of the most attractive approaches for 2-CA production. However, development of the bioprocess was plagued by low activity of amidase for 2-chloronicotinamide. In this work, an amidase signature (AS) family amidase from Pantoea sp. (Pa-Ami), with superior activity for nicotinamide and its chlorinated derivatives, was exploited and characterized. Kinetic analysis and molecular docking clearly indicated that chlorine substitution in the pyridine ring of nicotinamide, especially the substitution at 2-position led to a dramatic decrease of Pa-Ami activity. The productivity of the bioprocess was significantly improved using fed-batch mode at low reaction temperature and 2-CA was produced as high as 370 mM with a substrate conversion of 94.2%. These results imply that Pa-Ami is potentially promising biocatalyst for industrial production of 2-CA.

Process development for efficient biosynthesis of L-DOPA with recombinant Escherichia coli harboring tyrosine phenol lyase from Fusobacterium nucleatum.

The tyrosine phenol lyase (TPL) catalyzed synthesis of L-DOPA was regarded as one of the most economic route for L-DOPA synthesis. In our previous study, a novel TPL from Fusobacterium nucleatum (Fn-TPL) was exploited for efficient biosynthesis of L-DOPA. However, the catalytic efficiency decreased when the reaction system expanded from 100 mL to 1 L. As such, the bioprocess for scale-up production of L-DOPA was developed in this study. To increase the stability of substrate and product, as well as decrease the by-product formation, the optimum temperature and pH were determined to be 15 °C and pH 8.0, respectively. The initial concentration of pyrocatechol, pyruvate and ammonium acetate was fixed at 8, 5 and 77 g/L and a fed-batch approach was applied with sodium pyruvate, pyrocatechol and ammonium acetate fed in a concentration of 5, 5 and 3.5 g/L, respectively. In addition, L-DOPA crystals were exogenously added to inhibit cell encapsulation by the precipitated product. The final L-DOPA concentration reached higher than 120 g/L with pyrocatechol conversion more than 96% in a 15-L stirred tank, demonstrating the great potential of Fn-TPL for industrial production of L-DOPA.

Rate-limiting steps in the Saccharomyces cerevisiae ergosterol pathway: towards improved ergosta-5,7-dien-3ß-ol accumulation by metabolic engineering.

Ergosterol is the predominant nature sterol constituent of plasma membrane in Saccharomyces cerevisiae. Herein, the biosynthetic pathway of ergosterol was proposed to be metabolically engineered for the efficient production of ergosta-5,7-dien-3ß-ol, which is the precursor of vitamin D4. By target disruption of erg5, involved in the end-steps of post-squalene formation, predominantly accumulated ergosta-5,7-dien-3ß-ol (4.12 mg/g dry cell weight). Moreover, the rate-limiting enzymes of ergosta-5,7-dien-3ß-ol biosynthesis were characterized. Overexpression of Hmg1p led to a significant accumulation of squalene, and induction of Erg1p/Erg11p expression raised the yield of both total sterols and ergosta-5,7-dien-3ß-ol with no obvious changes in growth behavior. Furthermore, the transcription factor allele upc2-1 was overexpressed to explore the effect of combined induction of rate-limiting enzymes. Compared with an obviously enhanced yield of ergosterol in the wild-type strain, decreases of both the ergosta-5,7-dienol levels and the total sterol yield were found in Δerg5-upc2-1, probably due to the unbalanced NADH/NAD+ ratio observed in the erg5 knockouts, suggesting the whole-cell redox homeostasis was also vital for end-product biosynthesis. The data obtained in this study can be used as reference values for the production of sterol-related intermediates involved in the post-squalene biosynthetic pathway in food-grade S. cerevisiae strains.