A KetoREDuctase (KRED) engineered via directed evolution technologies catalyzed the asymmetric reduction of (E)-methyl 2-(3-(3-(2-(7-chloroquinolin-2-yl)vinyl)phenyl)-3-oxopropyl)benzoate to the corresponding (S)-alcohol, a key intermediate in the synthesis of montelukast sodium (Singulair). Through synergistic efforts in process chemistry, molecular biology, bioinformatics and high throughput screening, a KRED with very high enantioselectivity (>99.9% ee) was developed for an economical and simple process that takes advantage of the physical properties of the substrate and product. The evolved KRED is an efficient and robust enzyme for catalyzing the reaction of an essentially water insoluble substrate (c log P ≈ 7) at a 100 g/L loading in the presence of ∼70% organic solvents at 45 °C. The biocatalytic process currently runs at >200 kg scale.
Cysteine is the major source of fixed sulfur for the synthesis of sulfur-containing compounds in organisms of the Bacteria and Eucarya domains. Though pathways for cysteine biosynthesis have been established for both of these domains, it is unknown how the Archaea fix sulfur or synthesize cysteine. None of the four archaeal genomes sequenced to date contain open reading frames with identities to either O-acetyl-L-serine sulfhydrylase (OASS) or homocysteine synthase, the only sulfur-fixing enzymes known in nature. We report the purification and characterization of OASS from acetate-grown Methanosarcina thermophila, a moderately thermophilic methanoarchaeon. The purified OASS contained pyridoxal 5-phosphate and catalyzed the formation of L-cysteine and acetate from O-acetyl-L-serine and sulfide. The N-terminal amino acid sequence has high sequence similarity with other known OASS enzymes from the Eucarya and Bacteria domains. The purified OASS had a specific activity of 129 mol of cysteine/min/mg, with a K m of 500 ؎ 80 M for sulfide, and exhibited positive cooperativity and substrate inhibition with O-acetyl-L-serine. Sodium dodecyl sulfatepolyacrylamide gel electrophoresis revealed a single band at 36 kDa, and native gel filtration chromatography indicated a molecular mass of 93 kDa, suggesting that the purified OASS is either a homodimer or a homotrimer. The optimum temperature for activity was between 40 and 60°C, consistent with the optimum growth temperature for M. thermophila. The results of this study provide the first evidence for a sulfur-fixing enzyme in the Archaea domain. The results also provide the first biochemical evidence for an enzyme with the potential for involvement in cysteine biosynthesis in the Archaea.The serine and homoserine pathways are the two major routes for cysteine biosynthesis in nature. Serine transacetylase and O-acetylserine sulfhydrylase (OASS) catalyze steps in the serine pathway (reactions 1 and 2) (28):Homoserine transacetylase, homocysteine synthase, cystathionine -synthase, and ␥-cystathionase catalyze steps of the homoserine pathway (reactions 3 to 6) (28):L-homocysteineϩserine3cystathionine
BackgroundIn recent years, much attention has been given to the spread of influenza around the world. With the continuing human outbreak of H5N1 beginning in 2003 and the H1N1 pandemic in 2009, focus on influenza and other respiratory viruses has been increased. It has been accepted for decades that international travel via jet aircraft is a major vector for global spread of influenza, and epidemiological differences between tropical and temperate regions observed. Thus we wanted to study how indoor environmental conditions (enclosed locations) in the tropics and winter temperate zones contribute to the aerosol spread of influenza by travelers. To this end, a survey consisting of 632 readings of temperature (T) versus relative humidity (RH) in 389 different enclosed locations air travelers are likely to visit in 8 tropical nations were compared to 102 such readings in 2 Australian cities, including ground transport, hotels, shops, offices and other publicly accessible locations, along with 586 time course readings from aircraft.ResultsAn influenza transmission risk contour map was developed for T versus RH. Empirical equations were created for estimating: 1. risk relative to temperature and RH, and 2. time parameterized influenza transmission risk. Using the transmission risk contours and equations, transmission risk for each country's locations was compared with influenza reports from the countries. Higher risk enclosed locations in the tropics included new automobile transport, luxury buses, luxury hotels, and bank branches. Most temperate locations were high risk.ConclusionEnvironmental control is recommended for public health mitigation focused on higher risk enclosed locations. Public health can make use of the methods developed to track potential vulnerability to aerosol influenza. The methods presented can also be used in influenza modeling. Accounting for differential aerosol transmission using T and RH can potentially explain anomalies of influenza epidemiology in addition to seasonality in temperate climates.
Two pathways for cysteine biosynthesis are known in nature; however, it is not known which, if either, the Archaea utilize. Enzyme activities in extracts of Methanosarcina thermophila grown with combinations of cysteine and sulfide as sulfur sources indicated that this archaeon utilizes the pathway found in the Bacteria domain. The genes encoding serine transacetylase and O-acetylserine sulfhydrylase (cysE and cysK) are adjacent on the chromosome of M. thermophila and possibly form an operon. When M. thermophila is grown with cysteine as the sole sulfur source, O-acetylserine sulfhydrylase activity is maximally expressed suggesting alternative roles for this enzyme apart from cysteine biosynthesis. ß
Two pathways for cysteine biosynthesis are known in nature; however, it is not known which, if either, the Archaea utilize. Enzyme activities in extracts of Methanosarcina thermophila grown with combinations of cysteine and sulfide as sulfur sources indicated that this archaeon utilizes the pathway found in the Bacteria domain. The genes encoding serine transacetylase and O-acetylserine sulfhydrylase (cysE and cysK) are adjacent on the chromosome of M. thermophila and possibly form an operon. When M. thermophila is grown with cysteine as the sole sulfur source, O-acetylserine sulfhydrylase activity is maximally expressed suggesting alternative roles for this enzyme apart from cysteine biosynthesis.
Biocatalytic processes are of increasing importance in the production of chiral alcohols which are important building blocks in the synthesis of chemical catalysts, liquid crystals, agrochemicals and pharmaceuticals. Methods for the synthesis of chiral alcohols can be subdivided into three general classes: traditional (such as classic racemic resolution, chromatography, chiral pool synthesis), asymmetric chemical, and biological (enzymes, whole microbial cells) methods. The last can also be applied to the more traditional methods. Enzymatic techniques are attracting a growing interest as green catalysts because of the different advantages they offer, as compared to other methods: high selectivity, high product purity, mild reaction conditions, competitive production costs, and excellent catalyst availability. In this contribution we give an overview of the biocatalytic approaches for the manufacture of chiral alcohols. To our knowledge there are currently about five major enzyme groups applied for the synthesis of chiral alcohols. The first one reduces carbonyl functional groups (ketones) to enantiopure secondary alcohols (dehydrogenases or reductases). The second group forms alcohols by introduction of molecular oxygen with concomitant one or two electron reduction (mono‐ and dioxygenases). The third group forms alcohols by addition of water to unsaturated carbon carbon double bonds (hydratases) whereas the fourth one forms alcohols by nucleophilic addition of small molecules such as HCN at carbonyl groups which usually also results in a new C–C bond formation (hydroxynitrile lyases and aldolases). The last major group of enzymes discussed herein belongs to the traditional methods mentioned above and resolves racemic chiral alcohols by reacting with only one enantiomer in a racemic mixture (hydrolases). In a selection of case studies we demonstrate the high level of importance that biocatalytic processes have already gained in the industrial manufacture of chiral alcohols. There are numerous processes available that have been or still are operated in multi‐tonne scale. By solving the drawback of cofactor requirements and regeneration for a range of enzymes, especially in the area of asymmetric reduction, the dehydrogenases and oxygenases are now commonly used for commercial processes and are in several cases superior to whole‐cell microbial processes. The highly competitive nature of enzymatic processes compared to whole‐cell (fermentation) and chemical approaches is demonstrated with the example of the manufacture of optically active ethyl ( R )‐3‐hydroxybutyrate.
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