Klebsiella pneumoniae 1,3-propanediol:NAD+ oxidoreductase.

Fermentative utilization of glycerol, a more reduced carbohydrate than aldoses and ketoses, requires the disposal of the two extra hydrogen atoms. This is accomplished by sacrificing an equal quantity of glycerol via an auxiliary pathway initiated by glycerol dehydratase. The product, 3-hydroxypropionaldehyde, is then reduced by 1,3-propanediol NAD+:oxidoreductase (1,3-propanediol dehydrogenase; EC 1.1.1.202), resulting in the regeneration of NAD+ from NADH. The pathway for the assimilation of glycerol is initiated by an NAD-linked dehydrogenase. In Klebsiella pneumoniae the two pathways are encoded by the dha regulon which is inducible only anaerobically. In this study 1,3-propanediol:NAD+ oxidoreductase was purified from cells grown anaerobically on glycerol. The enzyme was immunochemically distinct from the NAD-linked glycerol dehydrogenase and was an octamer or hexamer of a polypeptide of 45,000 +/- 3,000 daltons. When tested as a dehydrogenase, only 1,3-propanediol served as a substrate; no activity was detected with ethanol, 1-propanol, 1,2-propanediol, glycerol, or 1,4-butanediol. The enzyme was inhibited by chelators of divalent cations. An enzyme preparation inhibited by alpha,alpha'-dipyridyl was reactivated by the addition of Fe2+ or Mn2+ after removal of the chelator by gel filtration. As for glycerol dehydrogenase, 1,3-propanediol oxidoreductase is apparently inactivated by oxidation during aerobic metabolism, under which condition the enzyme becomes superfluous.     

Purification, separation, and characterization of two molecular forms of D-1-amino-2-propanol:NAD+ oxidoreductase activity from extracts of Escherichia coli K-12.

D-1-Amino-2-propanol:NAD+ oxidoreductase activity, which catalyzes the second step in a pathway wherein L-threonine is converted to D-1-amino-2-propanol via the intermediate formation of aminoacetone, has been purified 500-fold from Escherichia coli K-12. Although the enzyme catalyzes the oxidation of certain diols as well as 1-amino-2-propanol, it is completely specific for the D-isomer of the amino alcohol and for NAD+. Two molecular forms (designated Form L and Form S) of the oxidoreductase, both of which are catalytically active, have been separated by gel filtration on Sephadex G-200; apparently, Form L is converted to Form S by dissociation (Form L leads to Form S). Molecular weight determinations indicate that the two forms of the enzyme are different not only in size but also in shape; Form L apparently is an asymmetric tetramer of Form S. The two molecular species have similar catalytic properties. Both exhibit the same pH optimum of 8.6, have nearly identical apparent Km values for substrate and cosubstrate, are equally sensitive to inhibition by p-mercuribenzoate and N-ethylmaleimide, and show the same specificity for cosubstrate. Neither form of the enzyme has an absolute requirement for added thiol compounds or divalent metal ions.     

1,3-Propanediol:NAD+ oxidoreductases of Lactobacillus brevis and Lactobacillus buchneri.

In the cofermentation of glycerol with a sugar by Lactobacillus brevis and Lactobacillus buchneri, a 1,3-propanediol:NAD+ oxidoreductase provides an additional method of NADH disposal. The enzyme has been purified from both L. brevis B22 and L. buchneri B190 and found to have properties very similar to those reported for the enzyme from Klebsiella pneumoniae. The enzymes required Mn2+ and are probably octamers with a molecular mass of 350 kDa. Although not absolutely specific for 1,3-propanediol when tested as dehydrogenases, the enzymes have less than 10% activity with glycerol, ethanol, and 1,2-propanediol. These properties contrast sharply with those of a protein isolated from another Lactobacillus species (L. reuteri) that ferments glycerol with glucose and previously designated a 1,3-propanediol dehydrogenase.     

1,3-Propanediol:NAD+ oxidoreductases of Lactobacillus brevis and Lactobacillus buchneri.

In the cofermentation of glycerol with a sugar by Lactobacillus brevis and Lactobacillus buchneri, a 1,3-propanediol:NAD+ oxidoreductase provides an additional method of NADH disposal. The enzyme has been purified from both L. brevis B22 and L. buchneri B190 and found to have properties very similar to those reported for the enzyme from Klebsiella pneumoniae. The enzymes required Mn2+ and are probably octamers with a molecular mass of 350 kDa. Although not absolutely specific for 1,3-propanediol when tested as dehydrogenases, the enzymes have less than 10% activity with glycerol, ethanol, and 1,2-propanediol. These properties contrast sharply with those of a protein isolated from another Lactobacillus species (L. reuteri) that ferments glycerol with glucose and previously designated a 1,3-propanediol dehydrogenase.     

D-1-amino-2-propanol:NAD+ oxidoreductase. Purification and general properties of the large molecular form of the enzyme from Escherichia coli K12

Growth of Escherichia coli K12 under relatively anaerobic conditions in a medium containing casein hydrolysate, 0.8% glycerol, and 0.8% hydroxyacetone has been found to induce the level of D-1-amino-2-propanol oxidoreductase activity 50- to 100-fold over that in cells grown in casein hydrolysate alone or with 0.8% glycerol added. A large molecular weight form of this oxidoreductase (designated Form L) has been purified to apparent homogeneity in good yield by three simple steps designed to obviate its conversion to a smaller species. The molecular weight of native Form L and its basic subunit are 417,000 +/- 20,700 and 50,500 +/- 2,770, respectively; hence Form L would appear to consist of eight identical subunits. The pH activity profile for Form L shows one optimum in the range of 8.3 to 8.6 and another at pH 10.0 to 10.2. This form of the oxidoreductase has no apparent requirement for added metal ions (rather, numerous divalent transition metal ions are strongly inhibitory) or thiol compounds; it catalyzes the oxidation of several vic-glycols but is completely stereospecific for the D-isomer of 1-amino-2-propanol, utilizes only NAD+ as cosubstrate in the oxidation reaction (Km for NAD+ with DL-1-amino-2-propanol = 1.23 mM), but both NADH and NADPH serve as cosubstrate in the reduction of hydroxyacetone. Oxidoreductase activity of Form L is highly sensitive to inhibition by Hg2+, p-mercuribenzoate, or dithiodipyridine; inhibition by the latter two compounds is completely reversed by adding a thiol in excess.     

Rhamnose-induced propanediol oxidoreductase in Escherichia coli: purification, properties, and comparison with the fucose-induced enzyme.

Escherichia coli are capable of growing anaerobically on L-rhamnose as a sole source of carbon and energy and without any exogenous hydrogen acceptor. When grown under such condition, synthesis of a nicotinamide adenine dinucleotide-linked L-lactaldehydepropanediol oxidoreductase is induced. The functioning of this enzyme results in the regeneration of nicotinamide adenine dinucleotide. The enzyme was purified to electrophoretic homogeneity. It has a molecular weight of 76,000, with two subunits that are indistinguishable by electrophoretic mobility. The enzyme reduces L-lactaldehyde to L-1,2-propanediol with reduced nicotinamide adenine dinucleotide as a cofactor. The Km were 0.035 mM L-lactaldehyde and 1.25 mM L-1,2-propanediol, at pH 7.0 and 9.5, respectively. The enzyme acts only on the L-isomers. Strong substrate inhibition was observed with L-1,2-propanediol (above 25 mM) in the dehydrogenase reaction. The enzyme has a pH optimum of 6.5 for the reduction of L-lactaldehyde and of 9.5 for the dehydrogenation of L-1,2-propanediol. The enzyme is, according to the parameters presented in this report, indistinguishable from the propanediol oxidoreductase induced by anaerobic growth on fucose.     

Enhanced production of (R)-1,2-propanediol by metabolically engineered Escherichia coli

1,2-Propanediol (1,2-PD) is a major commodity chemical currently derived from propylene. Previously, we have demonstrated the production of enantiomerically pure (R)-1,2-propanediol from glucose by an engineered E. coli expressing genes for NADH-linked glycerol dehydrogenase and methylglyoxal synthase. In this work, we investigate three methods to improve 1,2-PD in E. coli. First, we investigated improving the host by eliminating production of a byproduct, lactate. To do this, we constructed strains with mutations in two enzymes involved in lactate production, lactate dehydrogenase and glyoxalase I. (Surprisingly, when mutations were made in its ability to produce lactate, one strain of E. coli [MM294], produced a small amount of 1,2-PD without any added genes.) Second, we constructed a complete pathway to 1,2-PD from the glycolytic intermediate, dihydroxyacetone phosphate. Our previous 1, 2-PD producing strains relied on at least one endogenous E. coli activity and only produced 0.7 g/L of 1,2-PD. The complete pathway involved the coexpression of methylglyoxal synthase (mgs), glycerol dehydrogenase (gldA), and either yeast alcohol dehydrogenase (adhI) or E. coli 1,2-propanediol oxidoreductase (fucO). Third, we investigated bioprocessing improvements by carrying out a fed-batch fermentation with the best engineered strain (expressing mgs, gldA, and fucO). A final titer of 4.5 g/L of (R)-1,2-PD was produced, with a final yield of 0.19 g of 1,2-PD per gram of glucose consumed. This work provides a basis for further strain and process improvement.     

Ferrous-activated nicotinamide adenine dinucleotide-linked dehydrogenase from a mutant of Escherichia coli capable of growth on 1, 2-propanediol

A nicotinamide adenine dinucleotide-linked dehydrogenase has been partially purified from a mutant of Escherichia coli K-12 able to grow on l-1,2-propanediol as carbon and energy source. This enzyme catalyzes the dehydrogenation at carbon 1 of l-1,2-propanediol, glycerol, 1,3-propanediol, ethylene glycol, and ethyl alcohol. The purified protein requires added ferrous or managanous ions. The V(max) and the apparent K(m) for a given substrate vary with the particular metal used.     

pH对克雷伯氏菌1,3-丙二醇合成关键酶酶活及发酵特性的影响

在5 L发酵罐进行甘油脉冲流加发酵,分析了不同pH值对克雷伯氏肺炎杆菌发酵特性的影响,pH 6.5为菌体最佳生长条件,克雷伯氏肺炎杆菌合成1,3-丙二醇的产量最高。在1,3-丙二醇合成速率较大的对数中前期,进行甘油脉冲流加发酵,提高甘油浓度促进甘油脱水酶、1,3-丙二醇氧化还原酶和甘油脱氢酶活性。不同pH值的脉冲试验表明,甘油脱水酶,2,3-丁二醇脱氢酶比酶活随着pH值的升高而升高,1,3-丙二醇氧化还原酶,乳酸脱氢酶比酶活在pH6.5最高,因此偏酸性的发酵条件和对数期维持一定的甘油浓度能够促进1,3-丙二醇的合成。     

克雷伯杆菌甘油脱氢酶和1,3-丙二醇氧化还原酶的动力学机制

本研究主要对克雷伯杆菌甘油转化1,3-丙二醇代谢途径中的2个关键酶甘油脱氢酶(GDH)、1,3-丙二醇氧化还原酶(PDOR)反应机制和动力学进行了研究。首先,通过初速度和产物抑制动力学研究确定了GDH、PDOR双底物酶促反应机制为有序BiBi机制,明确了由反应物消耗到产物生成之间的历程。其次,建立了GDH、PDOR双底物酶促反应动力学模型,由动力学模型可知,在偶合反应中,如果GDH和PDOR酶量相同,GDH氧化反应成为限速反应,而辅酶I将主要以氧化型NAD+形式存在。动力学信息为酶法合成1,3-丙二醇和代谢工程研究提供理论指导。     

High-level expression of the 1,3-propanediol oxidoreductase from klebsiella pneumoniae in escherichia coli

As one of four key enzymes in glycerol dismutation process, 1,3-propanediol oxidoreductase (EC.1.1.1.202) is important in converting glycerol to 1,3-propanediol in Klebsiella pneumoniae. The dhaT gene encoding 1,3-propanediol oxidoreductase was amplified by polymerase chain reaction (PCR) using the genome DNA of K. pneumoniae as template, and then cloned into cloning vector pMD18-T. After DNA sequence was determined, the dhaT gene was subcloned into Escherichia coli expression vector pET-22b (+) and pET-28a (+). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed that both the recombinant E. coli BL21 (DE3) (pET-22b (+)-dhaT) and E. coli BL21(DE3)(pET-28a (+)-dhaT) expressed predicted 42-kDa 1,3-propanediol oxidoreductase after induced by isopropyl-β-d-thiogalactopyranoside (IPTG), and the recombinant enzyme of E. coli BL21 (DE3) (pET-28a (+)-dhaT) was mostly in soluble form, and exhibited high activity (96.8 U/mL culture). The recombinant enzyme was purified and biochemically characterized. The apparent K _m values of the enzyme for 1,3-propanediol and NAD⁺ were 8.5 and 0.21 mM, respectively. The enzyme had maximum activity at pH 9.5 and 30°C.     

Evolution of propanediol utilization in Escherichia coli: mutant with improved substrate-scavenging power.

Wild-type strains of Escherichia coli are unable to use L-1,2-propanediol as a carbon and energy source. A series of mutants, able to grow on this compound at progressively faster rates, had been isolated by repeated transfers to a medium containing 20 mM L-1,2-propanediol. These strains synthesize at high constitutive levels a propanediolmicotinamide adenine dinucleotide oxidoreductase, an enzyme serving as a lactaldehyde during L-fucose fermentation by wild type cells. In this study, a mutant that can grow rapidly on the novel carbon source was subjected to further selection in a medium containing L-1,2-propanediol never exceeding 0.5 mM to obtain a derivative that has an increased power to extract the substrate from the medium. The emerging mutant exhibited four changes at the enzymatic level: (i) fuculose 1-phosphate aldolase activity is lost; (ii) the constitutive propanediol oxidoreductase activity is increased in its level; (iii) lactaldehyde dehydrogenase becomes constitutive and shows an elevated specific activity in crude extracts; and (iv) at low concentrations of propanediol, the facilitated diffusion across the cell membrane is enhanced. Changes two to four seem to act in concert in the trapping of propanediol by hastening its rate of entry and conversion to an ionized metabolite, lactate.     

Growth on D-arabitol of a mutant strain of Escherichia coli K12 using a novel dehydrogenase and enzymes related to L-1,2-propanediol and D-xylose metabolism.

Escherichia coli K12 cannot grow on D-arabitol, L-arabitol, ribitol or xylitol (Reiner, 1975). Using a mutant of E. coli K12 (strain 3; Sridhara et al., 1969) that can grow on L-1,2-propanediol, a second-stage mutant was isolated which can utilize D-arabitol as sole source of carbon and energy for growth. D-Arabitol is probably transported into the bacteria by the same system as that used for the transport of L-1,2-propanediol. The second-stage mutant constitutively synthesizes a new dehydrogenase, which is not present in the parent strain 3. This enzyme, whose native substrate may be D-galactose, apparently dehydrogenates D-arabitol to D-xylulose, and its structural gene is located at 68.5 +/- 1 min on the E. coli genetic map. D-Xylulose is subsequently catabolized by the enzymes of the D-xylose metabolic pathway.     

Inactivation of glycerol dehydrogenase of Klebsiella pneumoniae and the role of divalent cations.

Anaerobically induced NAD-linked glycerol dehydrogenase of Klebsiella pneumoniae for fermentative glycerol utilization was reported previously to be inactivated in the cell during oxidative metabolism. In vitro inactivation was observed in this study by incubating the purified enzyme in the presence of O2, Fe2+, and ascorbate or dihydroxyfumarate. It appears that O2 and the reducing agent formed H2O2 and that H2O2 reacted with Fe2+ to generate an activated species of oxygen which attacked the enzyme. The in vitro-oxidized enzyme, like the in vivo-inactivated enzyme, showed an increased Km for NAD (but not glycerol) and could no longer be activated by Mn2+ which increased the Vmax of the native enzyme but decreased its apparent affinity for NAD. Ethanol dehydrogenase and 1,3-propanediol oxidoreductase, two enzymes with anaerobic function, also lost activity when the cells were incubated aerobically with glucose. However, glucose 6-phosphate dehydrogenase (NADP-linked), isocitrate dehydrogenase, and malate dehydrogenase, expected to function both aerobically and anaerobically, were not inactivated. Thus, oxidative modification of proteins in vivo might provide a mechanism for regulating the activities of some anaerobic enzymes.     

Employing bacterial microcompartment technology to engineer a shell-free enzyme-aggregate for enhanced 1,2-propanediol production in Escherichia coli

Bacterial microcompartments (BMCs) enhance the breakdown of metabolites such as 1,2-propanediol (1,2-PD) to propionic acid. The encapsulation of proteins within the BMC is mediated by the presence of targeting sequences. In an attempt to redesign the Pdu BMC into a 1,2-PD synthesising factory using glycerol as the starting material we added N-terminal targeting peptides to glycerol dehydrogenase, dihydroxyacetone kinase, methylglyoxal synthase and 1,2-propanediol oxidoreductase to allow their inclusion into an empty BMC. 1,2-PD producing strains containing the fused enzymes exhibit a 245% increase in product formation in comparison to un-tagged enzymes, irrespective of the presence of BMCs. Tagging of enzymes with targeting peptides results in the formation of dense protein aggregates within the cell that are shown by immuno-labelling to contain the vast majority of tagged proteins. It can therefore be concluded that these protein inclusions are metabolically active and facilitate the significant increase in product formation.     

Utilization of Glycerol as a Hydrogen Acceptor by Lactobacillus reuteri: Purification of 1,3-Propanediol:NAD+ Oxidoreductase

Lactobacillus reuteri utilizes exogenously added glycerol as a hydrogen acceptor during carbohydrate fermentations, resulting in higher growth rates and cell yields than those obtained during growth on carbohydrates alone. Glycerol is first converted to 3-hydroxypropionaldehyde by a coenzyme B₁₂-dependent glycerol dehydratase and then reduced to 1,3-propanediol by an NAD⁺ -dependent oxidoreductase. The latter enzyme was purified and determined to have a molecular weight of 180,000; it is predicted to exist as a tetramer of identical 42,000-molecular-weight subunits.     

Characterization and expression of the plasmid-borne bedD gene from Pseudomonas putida ML2, which codes for a NAD+-dependent cis-benzene dihydrodiol dehydrogenase.

The catabolic plasmid pHMT112 in Pseudomonas putida ML2 contains the bed gene cluster encoding benzene dioxygenase (bedC1C2BA) and a NAD+-dependent dehydrogenase (bedD) required to convert benzene into catechol. Analysis of the nucleotide sequence upstream of the benzene dioxygenase gene cluster (bedC1C2BA) revealed a 1,098-bp open reading frame (bedD) flanked by two 42-bp direct repeats, each containing a 14-bp sequence identical to the inverted repeat of IS26. In vitro translation analysis showed bedD to code for a polypeptide of ca. 39 kDa. Both the nucleotide and the deduced amino acid sequences show significant identity to sequences of glycerol dehydrogenases from Escherichia coli, Citrobacter freundii, and Bacillus stearothermophilus. A bedD mutant of P. putida ML2 in which the gene was disrupted by a kanamycin resistance cassette was unable to utilize benzene for growth. The bedD gene product was found to complement the todD mutation in P. putida 39/D, the latter defective in the analogous cis-toluene dihydrodiol dehydrogenase. The dehydrogenase encoded by bedD) was overexpressed in Escherichia coli and purified. It was found to utilize NAD+ as an electron acceptor and exhibited higher substrate specificity for cis-benzene dihydrodiol and 1,2-propanediol compared with glycerol. Such a medium-chain dehydrogenase is the first to be reported for a Pseudomonas species, and its association with an aromatic ring-hydroxylating dioxygenase is unique among bacterial species capable of metabolizing aromatic hydrocarbons.     

Utilization of Glycerol as a Hydrogen Acceptor by Lactobacillus reuteri: Purification of 1,3-Propanediol:NAD Oxidoreductase

Lactobacillus reuteri utilizes exogenously added glycerol as a hydrogen acceptor during carbohydrate fermentations, resulting in higher growth rates and cell yields than those obtained during growth on carbohydrates alone. Glycerol is first converted to 3-hydroxypropionaldehyde by a coenzyme B(12)-dependent glycerol dehydratase and then reduced to 1,3-propanediol by an NAD -dependent oxidoreductase. The latter enzyme was purified and determined to have a molecular weight of 180,000; it is predicted to exist as a tetramer of identical 42,000-molecular-weight subunits.     

Isolation of a sn-glycerol 3-phosphate: NAD oxidoreductase from spinach leaves.

An NAD-dependent glycerol 3-phosphate dehydrogenase (sn-glycerol 3-phosphate: NAD oxidoreductase; EC 1.1.1.8) has been purified from spinach leaves by a three-step procedure involving ion-exchange, gel filtration, and affinity chromatography. The enzyme has been purified over 10,000-fold to a specific activity of 38. It has a molecular weight of approximately 63,500. The pH optimum for the reduction of dihydroxyacetone phosphate is 6.8 and for glycerol 3-phosphate oxidation it is 9.5. During dihydroxyacetone phosphate reduction hyperbolic kinetics were observed when either NADH or dihydroxyacetone phosphate was the variable substrate, but concentrations of NADH greater than 150 μm were inhibitory. Michaelis constants were 0.30–0.35 mm for dihydroxyacetone phosphate and 0.01 mm for NADH. Glycerol 3-phosphate oxidation obeyed Michaelis-Menten kinetics with a K_m of 0.19 mm for NAD and 1.6 mm for glycerol 3-phosphate. The enzyme was specific for those substrates, and dihydroxyacetone, glyceraldehyde, glyceraldehyde 3-phosphate, NADPH, NADP, and glycerol were not utilized. The spinach leaf enzyme appears to be in the cytoplasm and probably functions for the production of glycerol 3-phosphate from dihydroxyacetone phosphate.