Betaine supplementation improved L-threonine fermentation of Escherichia coli THRD by upregulating zwf (glucose-6-phosphate dehydrogenase) expression

BACKGROUND: The supplementation of betaine, an osmoprotective compatible solute, in the cultivation media has been widely used to protect bacterial cells. To explore the effects of betaine addition on industrial fermentation, Escherichia coli THRD, an L-threonine producer, was used to examine the production of L-threonine with betaine supplementation and the underlying mechanism through which betaine functions was investigated. RESULTS: Betaine supplementation in the medium of E. coli THRD significantly improved L-threonine fermentation parameters. The transcription of zwf and corresponding enzyme activity of glucose-6-phosphate dehydrogenase were significantly promoted by betaine addition, which contributed to an enhanced expression of zwf that provided more nicotinamide adenine dinucleotide phosphate (NADPH) for L-threonine synthesis. In addition, as a result of the betaine addition, the betaine-stimulated expression of enhanced green fluorescent protein (eGFP) under the zwf promoter within a plasmid-based cassette proved to be a transcription-level response of zwf. Finally, the promoter of the phosphoenolpyruvate carboxylase gene ppc in THRD was replaced with that of zwf, while L-threonine fermentation of the new strain was promoted by betaine addition. Conclusions: We reveal a novel mode of betaine that facilitates the microbial production of useful compounds. Betaine supplementation upregulates the expression of zwf and increases the NADPH synthesis, which may be beneficial for the cell growth and thereby promote the production of L-threonine. This finding might be useful for the production of NADPH-dependent amino acids and derivatives in E. coli THRD or other E. coli strains.

Theoretical studies on the pyridoxal-5'-phosphate dependent enzyme dopa decarboxylase: Effect of Thr 246 residue on the co-factor-enzyme binding and reaction mechanism.

Decarboxylation of amino acid is a key step for biosynthesis of several important cellular metabolites in the biological systems. This process is catalyzed by amino acid decarboxylases and most of them use pyridoxal-5'-phosphate (PLP) as a co-factor. PLP is bound to the active site of the enzyme by various interactions with the neighboring amino acid residues. In the present investigation, density functional theory (DFT) and real-time dynamics studies on both ligand-free and ligand-bound dopa decarboxylases (DDC) have been carried out in order to elucidate the factors responsible for facile decarboxylation and also for proper binding of PLP in the active site of the enzyme. It has been found that in the crystal structure Asp271 interacts with the pyridine nitrogen atom of PLP through H-bonding in both native and substrate-bound DDC. On the contrary, Thr246 is in close proximity to the oxygen of 3-OH of PLP pyridine ring only in the substrate-bound DDC. In the ligand-free enzyme, the distance between the oxygen atom of 3-OH group of PLP pyridine ring and oxygen atom of Thr246 hydroxyl group is not favorable for hydrogen bonding. Thus, present study reveals that hydrogen bonding with O3 of PLP with a hydrogen bond donor residue provided by the enzyme plays an important role in the decarboxylation process.

Transient phosphorylation of tumor associated microtubule associated protein (TMAP)/cytoskeleton associated protein 2 (CKAP2) at Thr-596 during early phases of mitosis

Tumor associated microtubule associated protein (TMAP), also known as cytoskeleton associated protein 2 (CKAP2) is a mitotic spindle-associated protein whose expression is cell cycle-regulated and also frequently deregulated in cancer cells. Two monoclonal antibodies (mAbs) against TMAP/CKAP2 were produced: B-1-13 and D-12-3. Interestingly, the reactivity of mAb D-12-3 to TMAP/CKAP2 was markedly decreased specifically in mitotic cell lysate. The epitope mapping study showed that mAb D-12-3 recognizes the amino acid sequence between 569 and 625 and that phosphorylation at T596 completely abolishes the reactivity of the antibody, suggesting that the differential reactivity originates from the phosphorylation status at T596. Immunofluorescence staining showed that mAb D-12-3 fails to detect TMAP/CKAP2 in mitotic cells between prophase and metaphase, but the staining becomes evident again in anaphase, suggesting that phosphorylation at T596 occurs transiently during early phases of mitosis. These results suggest that the cellular functions of TMAP/CKAP2 might be regulated by timely phosphorylation and dephosphorylation during the course of mitosis.

Structure and function of enzymes involved in the anaerobic degradation of L-threonine to propionate.

In Escherichia coli and Salmonella typhimurium, L-threonine is cleaved non-oxidatively to propionate via 2-ketobutyrate by biodegradative threonine deaminase, 2-ketobutyrate formate-lyase (or pyruvate formate-lyase), phosphotransacetylase and propionate kinase. In the anaerobic condition, L-threonine is converted to the energy-rich keto acid and this is subsequently catabolised to produce ATP via substrate-level phosphorylation, providing a source of energy to the cells. Most of the enzymes involved in the degradation of L-threonine to propionate are encoded by the anaerobically regulated tdc operon. In the recent past, extensive structural and biochemical studies have been carried out on these enzymes by various groups. Besides detailed structural and functional insights, these studies have also shown the similarities and differences between the other related enzymes present in the metabolic network. In this paper, we review the structural and biochemical studies carried out on these enzymes.

The importance of the Thr17 residue of phospholamban as a phosphorylation site under physiological and pathological conditions

The sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) is under the control of an SR protein named phospholamban (PLN). Dephosphorylated PLN inhibits SERCA2a, whereas phosphorylation of PLN at either the Ser16 site by PKA or the Thr17 site by CaMKII reverses this inhibition, thus increasing SERCA2a activity and the rate of Ca2+ uptake by the SR. This leads to an increase in the velocity of relaxation, SR Ca2+ load and myocardial contractility. In the intact heart, ß-adrenoceptor stimulation results in phosphorylation of PLN at both Ser16 and Thr17 residues. Phosphorylation of the Thr17 residue requires both stimulation of the CaMKII signaling pathways and inhibition of PP1, the major phosphatase that dephosphorylates PLN. These two prerequisites appear to be fulfilled by ß-adrenoceptor stimulation, which as a result of PKA activation, triggers the activation of CaMKII by increasing intracellular Ca2+, and inhibits PP1. Several pathological situations such as ischemia-reperfusion injury or hypercapnic acidosis provide the required conditions for the phosphorylation of the Thr17 residue of PLN, independently of the increase in PKA activity, i.e., increased intracellular Ca2+ and acidosis-induced phosphatase inhibition. Our results indicated that PLN was phosphorylated at Thr17 at the onset of reflow and immediately after hypercapnia was established, and that this phosphorylation contributes to the mechanical recovery after both the ischemic and acidic insults. Studies on transgenic mice with Thr17 mutated to Ala (PLN-T17A) are consistent with these results. Thus, phosphorylation of the Thr17 residue of PLN probably participates in a protective mechanism that favors Ca2+ handling and limits intracellular Ca2+ overload in pathological situations.

Detection of an Ala601Thr Mutation of Plasminogen Gene in 3 out of 36 Korean Patients with Deep Vein Thrombosis

Plasminogen is a key proenzyme in the fibrinolytic and thrombolytic systems. Congenital deficiency of plasminogen and molecular abnormality of plasminogen (dysplasminogenemia) have been reported in association with the thrombotic tendency in human. In dysplasminogenemia, the level of immunoreactive plasminogen is normal, although the functional activity is reduced. Human plasminogen gene spans about 52.5 kb of DNA and consists of 19 exons. Three types of mutations (Ala601Thr, Val355Phe, and Asp676Asn) have been described in dysplasminogenemia. In this study, we measured the plasminogen activity in patients with deep vein thrombosis and analyzed the DNA sequence to detect three point mutations (Ala601Thr, Val355Phe and Asp676Asn) in patients with hypo/dysplasminogenemia. Dysplasminogenemia was identified in 3 (8.3%) of unrelated 36 patients with deep vein thrombosis and the Ala601Thr mutation was detected in all three patients with dysplasminogenemia. In conclusion, dysplasminogenemia is not rare in deep vein thrombosis, which suggests a risk factor for the thrombosis in Korean population.

Characterization of yeast deoxyhypusine synthase: PKC-dependent phosphorylation in vitro and functional domain identification

The biosynthesis of hypusine [Nepsilon-(4-amino-2-hydroxybutyl)-lysine] occurs in the eIF-5A precursor protein through two step posttranslational modification involving deoxyhypusine synthase which catalyzes transfer of the butylamine moiety of spermidine to the epsilon-amino group of a designated lysine residue and subsequent hydroxylation of this intermediate. This enzyme is exclusively required for cell viability and growth of yeast (Park, M.H. et al., J. Biol. Chem. 273: 1677-1683, 1998). In an effort to understand structure-function relationship of deoxyhypusine synthase, posttranslational modification(s) of the enzyme by protein kinases were carried out for a possible cellular modulation of this enzyme. And also twelve deletion mutants were constructed, expressed in E. coli system, and enzyme activities were examined. The results showed that deoxyhypusine synthase was phosphorylated by PKC in vitro but not by p56lck and p60c-src. Treatment with PMA specifically increased the relative phosphorylation of the enzyme supporting PKC was involved. Phosphoamino acid analysis of this enzyme revealed that deoxyhypusine synthase is mostly phosphorylated on serine residue and weakly on threonine. Removal of Met1-Glu10 (deltaMet1-Glu10) residues from amino terminal showed no effect on the catalytic activity but further deletion (deltaMet1-Ser20) caused loss of enzyme activity. The enzyme with internal deletion, deltaGln197-Asn212 (residues not present in the human enzyme) was found to be inactive. Removal of 5 residues from carboxyl terminal, deltaLys383-Asn387, retained only slight activity. These results suggested that deoxyhypusine synthase is substrate for PKC dependent phosphorylation and requires most of the polypeptide chains for enzyme activity except the first 15 residues of N-terminal despite of N- and C-terminal residues of the enzyme consist of variable regions. Copyright 2000 Academic Press.

Serine/threonine protein phosphatases and a protein phosphatase 1 inhibitor from Neurospora crassa

The major spontaneously active serine/threonine (Ser/Thr) protein phosphatase activities in N. crassa wild type (FGSC 424) were type 1 (PP1), type-2A (PP2A) and type-2C (PP2C). PP1 and PP2C predominantly dephosphorylated phosphorylase a and casein, respectively. PP2A acted on both substrates, but was two-fold more active against casein. PPI activity was inhibited by protamine, heparin, okadaic acid (IC50 50 nM) and mammalian inhibitor- 1 (lC50 2 nM). On the other hand, PP2A activity was inhibited by much lower concentrations of okadaic acid (IC50 0.2 nM) and also by protamine, but not by heparin or inhibitor-l. About 80 per cent of total PP1 activity was associated with the particulate fraction and could be partially extracted with 0.5 M NaCl. Seventy and ninety percent of PP2A and PP2C activities, respectively, were found in the soluble fraction. In addition we have partially purified an acid and thermostable PP1 inhibitor which effectively inhibits both N. crassa and mammalian PP1.

Hepatic mitochondrial membrane lipid environment and protein nutrition.

Effect of feeding rice diet with and without lysine and threonine supplementation on hepatic mitochondria and its inner and outer membrane proteins, enzymes and phospholipids has been studied. The exchange of phosphatidylcholine and phosphatidylethanolamine between microsomes and mitochondria has also been studied under these conditions. Deficient diet lead to significant decrease in proteins as well as activities of monoamine oxidase, succinate dehydrogenase, cytochrome a + a3 and cytochrome c in mitochondria and its inner and outer membranes. Feeding of the deficient diet also significantly reduced total phospholipids and PC in mitochondria and its outer mitochondrial membrane. In the inner mitochondrial membrane, only PE and cardiolipin were reduced. The incorporation (DPM/microgram PLP) of [methyl-3H]choline and [methyl-14C]methionine into PC of mitochondria and its outer membrane and that of 32Pi into PC and PE of outer mitochondrial membrane but only into PC of inner mitochondrial membrane were significantly reduced in the deficient group. The exchange rates of PC and PE between microsomes and mitochondria were reduced in the deficient group. Supplementation of the deficient diet with lysine and threonine profoundly improved the above biochemical lesions as compared to casein fed rats.

El enlace O-glicosídico en glicoproteínas de plasma seminal humano / The linkage O-glycosidic in glycoproteins of human seminal plasma

La composición y estructura de los extremos terminales no reductores portadores de los determinantes antigénicos en las cadenas de oligosacáridos de las glicoproteínas del plasma seminal humano, han permitido deducir que estos componentes son fragmentos producidos por la degradación proteolítica endógena de las mucinas. Dado que las cadenas de hidratos de carbono unidas O-glicosídicamente a la serina y la treonina de la cadena peptídica dan lugar a una reacción de beta-eliminación en condiciones alcalinas suaves, hicimos uso del tratamiento alcalino para demostrar la presencia de enlaces lábiles al álcali en las muestras de plasma seminal humano y algunas fracciones glicoproteicas aisladas a partir del mismo. El análisis de los hidratos de carbono que se liberan durante ell tratamiento han permitido obtener información sobre la composición y estructura de este tipo de unidades de oligosacarídos. Hemos identificado al monosacárido involucrado en el enlace O-glicosídico a serina y treonina y hemos podido caracterizar, a través de la reacción de beta-eliminación en condiciones reductoras y no reductoras, las unidades de monosacáridos del extremo terminal reductor