Cloning, expression, and characterization of cadmium and manganese uptake genes from Lactobacillus plantarum

An Mn(2+) and Cd(2+) uptake gene, mntA, was cloned from Lactobacillus plantarum ATCC 14917 into Escherichia coli. Its expression conferred on E. coli cells increased Cd(2+) sensitivity as well as energy-dependent Cd(2+) uptake activity. Both transcription and translation of mntA were induced by Mn(2+) starvation in L. plantarum, as indicated by reverse transcriptase PCR and immunoblotting. Two Cd(2+) uptake systems have been identified in L. plantarum: one is a high-affinity Mn(2+) and Cd(2+) uptake system that is expressed in Mn(2+)-starved cells, and the other is a nonsaturable Cd(2+) uptake system that is expressed in Cd(2+)-sufficient cells (Z. Hao, H. R. Reiske, and D. B. Wilson, Appl. Environ. Microbiol. 65:592-99, 1999). MntA was not detected in an Mn(2+)-dependent mutant of L. plantarum which had lost high-affinity Mn(2+) and Cd(2+) uptake activity. The results suggest that mntA is the gene encoding the high-affinity Mn(2+) and Cd(2+) transporter. On the basis of its predicted amino acid sequence, MntA belongs to the family of P-type cation-translocating ATPases. The topology and potential Mn(2+)- and Cd(2+)-binding sites of MntA are discussed. A second clone containing a low-affinity Cd(2+) transport system was also isolated.

Regulation of phenylalanine biosynthesis. Studies on the mechanism of phenylalanine binding and feedback inhibition in the Escherichia coli P-protein

Isothermal titration calorimetry (ITC) and site-directed mutagenesis were used to study the interaction of Phe with (a) the Escherichia coli P-protein, a bifunctional chorismate mutase/prephenate dehydratase that is feedback inhibited by Phe, (b) PDT32, a 32 kDa P-protein fragment (residues 101-386) containing the prephenate dehydratase and regulatory domains, and (c) R12, a C-terminal 12 kDa P-protein fragment (residues 286-386) containing the regulatory domain. DeltaH(total) values for PDT32, which included the heats of Phe binding, conformational change, and dimerization, established that in developing a mechanism for end product feedback inhibition, the P-protein has evolved a ligand recognition domain that exhibits Phe-binding enthalpies comparable to those reported for other full-fledged amino acid receptor proteins. Sequence alignments of R12 with other Phe-binding enzymes identified two highly conserved regions, GALV (residues 309-312) and ESRP (residues 329-332). Site-directed mutagenesis and ITC established that changes in the GALV and ESRP regions affected Phe binding and feedback inhibition to different extents. Mutagenesis further showed that C374 was essential for feedback inhibition, but not for Phe binding, while W338 was involved in Phe binding, but not in the Phe-induced conformational change required for feedback inhibition.

Second stage pushing correlates with headache after unintentional dural puncture in parturients

PURPOSE

To determine the association between bearing down, postdural puncture headache (PDPH) and epidural blood patch (EBP) following single 17 gauge unintentional dural puncture (UDP) in parturients.

METHODS

The charts of 60 parturients identified with UDP in our institutional database during epidural placement were independently reviewed. Patients were divided into categories based on the anesthetic record: well-documented single punctures; well-documented multiple punctures; catheter-related puncture; unclear category (not clear if more than one puncture occurred or if dural puncture had occurred at all) and no evidence of dural puncture. Patients with single 17 gauge punctures were divided into those who had pushed (Group 1) and those who had not (Group 2). Group 2 patients had undergone Cesarean section before reaching second stage labour. The incidence of PDPH, EBP, and cumulative duration to delivery after UDP were compared between groups.

RESULTS

Thirty-three patients with well-documented single punctures were identified: 23 had engaged in active pushing as part of second stage labour (Group 1); 10 had not (Group 2). Seventy-four percent of Group1I developed PDPH compared with 10% in Group 2 (P < 0.002). Fifty-seven percent of Group 1 received an EBP compared with 0% in Group 2 (P < 0.002). Increasing the duration of pushing was associated with an increasing incidence of PDPH; the majority of women who pushed > 30 min developed headache.

CONCLUSIONS

An increased incidence of PDPH and EBP after UDP occurs in women bearing down in 2nd stage labour when compared with those who never pushed. There was also an association between the cumulative duration of bearing down and the incidence of PDPH.

Estimated folate intakes: data updated to reflect food fortification, increased bioavailability, and dietary supplement use

BACKGROUND

There is a critical need to estimate dietary folate intakes for nutrition monitoring and food safety evaluations, but available intake data are seriously limited by several factors.

OBJECTIVE

Our objective was to update 2 national food consumption surveys to reflect folate intakes as a result of the recently initiated food fortification program and to correct folate intakes for the apparently higher bioavailability of synthetic folic acid (SFA; ie, folate added to foods or from dietary supplements) than of naturally occurring folate so as to express intakes as dietary folate equivalents.

DESIGN

It was not possible to chemically analyze foods, so adjustments were made to food-composition data by using information about food ingredients and characteristics. Total folate intakes were estimated for several sex and age groups by using the modified data coupled with dietary supplement use.

RESULTS

Within the limitations of the data, our findings suggested that 67-95% of the population met or surpassed the new estimated average requirement, depending on the sex and age group and survey. Nonetheless, some subgroups had estimated intakes below these standards. Estimated SFA intakes suggested that approximately 15-25% of children aged 1-8 y, depending on the survey, had intakes above the newly established tolerable upper intake level. We estimated that 68-87% of females of childbearing age had SFA intakes below the recommended intake of 400 microgram/d, depending on the age group and survey.

CONCLUSION

There is a need to explore ways to improve folate intakes in targeted subgroups, including females of childbearing age, while not putting other population groups at risk of excessive intakes.

Mechanistic studies of active site mutants of Thermomonospora fusca endocellulase E2

Endocellulase E2 from the thermophilic bacterium Thermomonospora fusca is a member of glycosyl-hydrolase family 6 and is active from pH 4 to 10. Enzymes in this family hydrolyze beta-1,4-glycosidic bonds with inversion of the stereochemistry at the anomeric carbon. The X-ray crystal structures of two family 6 enzymes have been determined, and four conserved aspartic acid residues are found in or near the active sites of both. These residues have been mutated in another family 6 enzyme, Cellulomonas fimi CenA, and evidence was found for both a catalytic acid and a catalytic base. The corresponding residues in E2 (D79, D117, D156, and D265) were mutated, and the mutant genes were expressed in Streptomyces lividans. The mutant enzymes were purified and assayed for activity on three cellulosic substrates and 2, 4-dinitrophenyl-beta-D-cellobioside. Activity on phosphoric acid-swollen cellulose was measured as a function of pH for selected mutant enzymes. Binding affinities for each mutant enzyme were measured for two fluorescent ligands and cellotriose, and circular dichroism spectra were recorded. The results show that the roles of D117 and D156 are the same as those for the corresponding residues in CenA; D117 is the catalytic acid, and D156 raises the pK(a) of D117. No specific function was assigned to the CenA residue corresponding to D79, but in E2, this residue also assists in raising the pK(a) of D117 and is important for catalytic activity. The D265N mutant retained 7% of the wild-type activity, indicating that this residue is not playing the role of the catalytic base. Experiments were conducted to rule out contamination of the D265 enzymes by either wild-type E2 or an endogenous S. lividans CMCase.

Reciprocal changes in the expression of transcription factors GATA-4 and GATA-6 accompany adrenocortical tumorigenesis in mice and humans

While certain genetic changes are frequently found in adrenocortical carcinoma cells, the molecular basis of adrenocortical tumorigenesis remains poorly understood. Given that the transcription factors GATA-4 and GATA-6 have been implicated in gene expression and cellular differentiation in a variety of tissues, including endocrine organs such as testis, we have now examined their expression in the developing adrenal gland, as well as in adrenocortical cell lines and tumors from mice and humans. Northern blot analysis and in situ hybridization revealed abundant GATA-6 mRNA in the fetal and postnatal adrenal cortex of the mouse. In contrast, little or no GATA-4 expression was detected in adrenal tissue during normal development. In vivo stimulation with ACTH or suppression with dexamethasone did not affect the expression of GATA-4 or GATA-6 in the murine adrenal gland. To assess whether changes in the expression of GATA-4 or GATA-6 accompany adrenocortical tumorigenesis, we employed an established mouse model. When gonadectomized, inhibin alpha/SV40 T-antigen transgenic mice develop adrenocortical tumors in a gonadotropin-dependent fashion. In striking contrast to the normal adrenal glands, GATA-6 mRNA was absent from adrenocortical tumors or tumor-derived cell lines, while GATA-4 mRNA and protein were abundantly expressed in the tumors and tumor cell lines. Analogous results were obtained with human tissue samples; GATA-4 expression was detected in human adrenocortical carcinomas but not in normal tissue, adenomas, or pheochromocytomas. Taken together these results suggest different roles for GATA-4 and GATA-6 in the adrenal gland, and implicate GATA-4 in adrenal tumorigenesis. Immunohistochemical detection of GATA-4 may serve as a useful marker in the differential diagnosis of human adrenal tumors.

Effect of labor analgesia on breastfeeding success

BACKGROUND

The effect of labor analgesia on breastfeeding success is not well defined. Some authors have hypothesized that labor analgesia may affect lactation success. The purpose of this observational study was to determine if intrapartum analgesia influenced breastfeeding success at 6 weeks postpartum in a setting that strongly supported breastfeeding.

METHODS

Healthy women with uncomplicated term pregnancies who planned to breastfeed consented to a telephone interview. We recorded demographic data, labor induction status, delivery mode, and analgesic medications. At between 6 and 8 weeks postpartum, patients were asked to describe breastfeeding use, problems encountered, solutions derived, sources of support and information, and satisfaction. We created a logistic regression model using intrapartum analgesia information and controlling for demographic factors previously correlated with lactation success.

RESULTS

We enrolled 189 women, contacted 177 women postpartum, and obtained complete data on 171 women. Of these, 59 percent received epidural analgesia, 72 percent breastfed fully, and 20 percent breastfed partially (> 50% of infant nutrition) at 6 weeks postpartum. After controlling for demographics and labor outcome, we could not demonstrate a correlation between breastfeeding success at 6 to 8 weeks and labor analgesia.

CONCLUSIONS

In a hospital that strongly promotes breastfeeding, epidural labor analgesia with local anesthetics and opioids does not impede breastfeeding success. We recommend that hospitals that find decreased lactation success in parturients receiving epidural analgesia reexamine their postdelivery care policies.

Characterization and cloning of celR, a transcriptional regulator of cellulase genes from Thermomonospora fusca

CelR, a protein that regulates transcription of cellulase genes in Thermomonospora fusca (Actinomycetaceae) was purified to homogeneity. A 6-kilobase NotI-SacI fragment of T. fusca DNA containing the celR gene was cloned into Esherichia coli and sequenced. The celR gene encodes a 340-residue polypeptide that is highly homologous to members of the GalR-LacI family of bacterial transcriptional regulators. CelR specifically binds to a 14-base pair inverted repeat, which has sequence similarity to the binding sites of other family members. This site is present in regions upstream of all six cellulase genes in T. fusca. The binding of CelR to the celE promoter is inhibited specifically by low concentrations of cellobiose (0.2-0.5 mM), the major end product of cellulases. The other sugars tested did not affect binding at equivalent or 50-fold higher concentrations. The results suggest that CelR may act as a repressor, and that the mechanism of induction involves a direct interaction of CelR with cellobiose.

Distinct roles for visceral endoderm during embryonic mouse development

The murine visceral endoderm is an extraembryonic cell layer that appears prior to gastrulation and performs critical functions during embryogenesis. The traditional role ascribed to the visceral endoderm entails nutrient uptake and transport. Besides synthesizing a number of specialized proteins that facilitate uptake, digestion, and secretion of nutrients, the extraembryonic visceral endoderm coordinates blood cell differentiation and vessel formation in the adjoining mesoderm, thereby facilitating efficient exchange of nutrients and gases between the mother and embryo. Recent studies suggest that in addition to this nutrient exchange function the visceral endoderm overlying the egg cylinder stage embryo plays an active role in guiding early development. Cells in the anterior visceral endoderm function as an early organizer. Prior to formation of the primitive streak, these cells express specific gene products that specify the fate of underlying embryonic tissues. In this review we highlight recent investigations demonstrating this dual role for visceral endoderm as a provider of both nutrients and developmental cues for the early embryo.

Expression of an Aspergillus niger phytase gene (phyA) in Saccharomyces cerevisiae

Phytase improves the bioavailability of phytate phosphorus in plant foods to humans and animals and reduces phosphorus pollution of animal waste. Our objectives were to express an Aspergillus niger phytase gene (phyA) in Saccharomyces cerevisiae and to determine the effects of glycosylation on the phytase's activity and thermostability. A 1.4-kb DNA fragment containing the coding region of the phyA gene was inserted into the expression vector pYES2 and was expressed in S. cerevisiae as an active, extracellular phytase. The yield of total extracellular phytase activity was affected by the signal peptide and the medium composition. The expressed phytase had two pH optima (2 to 2.5 and 5 to 5.5) and a temperature optimum between 55 and 60 degrees C, and it cross-reacted with a rabbit polyclonal antibody against the wild-type enzyme. Due to the heavy glycosylation, the expressed phytase had a molecular size of approximately 120 kDa and appeared to be more thermostable than the commercial enzyme. Deglycosylation of the phytase resulted in losses of 9% of its activity and 40% of its thermostability. The recombinant phytase was effective in hydrolyzing phytate phosphorus from corn or soybean meal in vitro. In conclusion, the phyA gene was expressed as an active, extracellular phytase in S. cerevisiae, and its thermostability was affected by glycosylation.

Learning foraging thresholds for lizards: an analysis of a simple learning algorithm

This paper gives proof of convergence for a learning algorithm that describes how anoles (lizards found in the Caribbean) learn foraging threshold distance. An anole will pursue a prey if and only if it is within this threshold of the anole's perch. The learning algorithm was proposed by Roughgarden and his colleagues. They experimentally determined that this algorithm quickly converges to the foraging threshold that is predicted by optimal foraging theory. We provide analytic confirmation that the optimal foraging behavior as predicted by Roughgarden's model can be attained by a lizard that follows this simple and zoologically plausible rule of thumb. Copyright 1999 Academic Press.

Exploring immunological specificity using synthetic peptide combinatorial libraries

The definition of epitopes for human B and T cells is fundamental for the understanding of the immune response mechanism and its role in the prevention and cause of human disease. This understanding can be applied to the design of diagnostics and synthetic vaccines. In recent years, the understanding of the specificity of B and T cells has been advanced significantly by the development and use of combinatorial libraries made up of thousands to millions of synthetic peptides. The use of this approach has had four major effects: first, the definition of high affinity ligands both for T cells and antibodies; second, the application of alternative means for identifying immunologically relevant peptides for use as potential preventive and therapeutic vaccines; third, a new appreciation of the requirements for TCR interactions with peptide-MHC complexes in immunogenicity; fourth, the establishment of new principles regarding the level of cross-reactivity in immunological recognition.

Lumbar sympathetic blocks speed early and second stage induced labor in nulliparous women

BACKGROUND

Rapid cervical dilation reportedly accompanies lumbar sympathetic blockade, whereas epidural analgesia is associated with slow labor. The authors compared the effects of initial lumbar sympathetic block with those of epidural analgesia on labor speed and delivery mode in this pilot study.

METHODS

At a hospital not practicing active labor management, full-term nulliparous patients whose labors were induced randomly received initial lumbar sympathetic block or epidural analgesia. The latter patients received 10 ml bupivacaine, 0.125%; 50 microg fentanyl; and 100 microg epinephrine epidurally and sham lumbar sympathetic blocks. Patients to have lumbar sympathetic blocks received 10 ml bupivacaine, 0.5%; 25 microg fentanyl; and 50 microg epinephrine bilaterally and epidural catheters. Subsequently, all patients received epidural analgesia.

RESULTS

Cervical dilation occurred more quickly (57 vs. 120 min/cm cervical dilation; P = 0.05) during the first 2 h of analgesia in patients having lumbar sympathetic blocks (n = 17) than in patients having epidurals (n = 19). The second stage of labor was briefer in patients having lumbar sympathetic blocks than in those having epidurals (105 vs. 270 min; P < 0.05). Nine patients having lumbar sympathetic block and seven having epidurals delivered spontaneously, whereas seven patients having lumbar sympathetic block and seven having epidurals had instrument-assisted vaginal deliveries. Cesarean delivery for fetal bradycardia occurred in one patient having lumbar sympathetic block. Cesarean delivery for dystocia occurred in five patients having epidurals compared with no patient having lumbar sympathetic block (P = not significant). Visual analog pain scores differed only at 60 min after block.

CONCLUSIONS

Nulliparous parturients having induced labor and receiving initial lumbar sympathetic blocks had faster cervical dilation during the first 2 h of analgesia, shorter second-stage labors, and a trend toward a lower dystocia cesarean delivery rate than did patients having epidural analgesia. The effects of lumbar sympathetic block on labor need to be determined in other patient groups. These results may help define the tocodynamic effects of regional labor analgesia.

Regulatory T cells in experimental allergic encephalomyelitis. III. Comparison of disease resistance in Lewis and Fischer 344 rats

Rats of the Fischer 344 (F344) strain are resistant to experimental allergic encephalomyelitis (EAE) induced by active immunization with guinea pig myelin basic protein (MBP) in complete Freund's adjuvant whereas Lewis (LEW) rats are susceptible even though both strains share the same I-A-like class II alleles of the MHC RT1.B locus. To determine factors that might contribute to this difference in disease susceptibility, we have compared in these two strains (1) the frequency of MBP-reactive T cells in the lymph nodes and spleens of MBP-immunized animals, (2) the dominant MBP epitopes recognized by responding T cells, (3) the ability of MBP-reactive T cells to enter the central nervous system (CNS), and (4) the frequency of CD8+ regulatory T cells (RTC) whose activity is functionally antagonistic to MBP-reactive T cells. The results indicate that MBP-reactive T cell numbers are similar in MBP-immunized F344 and LEW rats, they both recognize p68-88 as the dominant encephalitogenic epitope of MBP, and MBP-reactive T cells isolated from immunized rats and adoptively transferred to naive animals are similarly effective in penetrating the blood-brain barrier and entering the CNS, leading to pathogenesis in EAE. However, the frequency of RTC that functionally inhibit MBP-reactive T cells is greater in F344 rats.

GATA4 haploinsufficiency in patients with interstitial deletion of chromosome region 8p23.1 and congenital heart disease

Previous studies have shown that patients with deletion of distal human chromosome arm 8p may have congenital heart disease and other physical anomalies. The gene encoding GATA-4, a zinc finger transcription factor implicated in cardiac gene expression and development, localizes to chromosome region 8p23.1. To examine whether GATA-4 deficiency is present in patients with monosomy of 8p23.1 with congenital heart disease, we performed fluorescence in situ hybridization (FISH) with a GATA4 probe on cells from a series of patients with interstitial deletion of 8p23.1. Four individuals with del(8)(p23.1) and congenital heart disease were found to be haploinsufficient at the GATA4 locus by FISH. The GATA4 gene was not deleted in a fifth patient with del(8)(p23.1) who lacked cardiac anomalies. FISH analysis on cells from 48 individuals with congenital heart disease and normal karyotypes failed to detect any submicroscopic deletions at the GATA4 locus. We conclude that haploinsufficiency at the GATA4 locus is often seen in patients with del(8)(p23.1) and congenital heart disease. Based on these findings and recent studies showing that haploinsufficiency for other cardiac transcription factor genes (e.g., TBX5, NKX2-5) causes congenital heart disease, we postulate that GATA-4 deficiency may contribute to the phenotype of patients with monosomy of 8p23.1.

Regulatory T cells in experimental allergic encephalomyelitis. I. Frequency and specificity analysis in normal and immune rats of a T cell subset that inhibits disease

We have shown previously that administration of myelin basic protein (MBP)-reactive T cells to naive Lewis rats induces not only autoimmune encephalomyelitis (EAE) but also a near total resistance to subsequent disease. By isolating the effector cells that are responsible for the resistance, we demonstrated that disease protection paralleled with increased numbers of a CD8+ regulatory T cell (RTC) subset and that co-injection of this RTC subset with encephalitogenic T cells aborted the pathogenic activity of the latter cells. Here, we show that a radio-sensitive splenic population of RTC also exists in naive rats that can be recruited and activated to inhibit the onset of secondary episodes of adoptive EAE. In co-transfer experiments, this protective RTC subpopulation can be isolated to neutralize the pathogenic activity of stimulatory MBP-reactive T cells in vivo. We show that the frequency of RTC with specificity for MBP-reactive T cells in naive rats is two orders of magnitude higher than the frequency of MBP-specific precursors, the activity of RTC increases substantially with age and RTC frequencies increase as a consequence of immunization with MBP-reactive cells lines. In specificity studies, we show that RTC isolated from naive rats and RTC from animals primed with one MBP-reactive cell line show cross-reactive responses to a variety of different MBP-reactive T cell lines. However, following repeated stimulation with a given MBP line, these RTC display a more limited, clonotypic response to the selecting line and assume a uniform CD8 phenotype. Finally, functional studies with RTC indicate that proliferative and lytic specificities do not necessarily correlate and that activated rat RTC are especially lytic for a Fas-sensitive murine cell line.

Expression and regulation of transcription factors GATA-4 and GATA-6 in developing mouse testis

Previous studies have shown that transcription factors GATA-4 and GATA-6 are expressed in granulosa and thecal cells of the mouse ovary and that GATA-4 expression in ovarian tissue is regulated by gonadotropins. Given the emerging role of GATA-4 and GATA-6 in gonadal cells, we have now studied the expression and regulation of these factors in the mouse testis and testicular cell lines. In situ hybridization demonstrated GATA-4 messenger RNA (mRNA) in the fetal testis at 13.5 days postcoitum. Both GATA-4 and GATA-6 transcripts were observed in late fetal, neonatal, juvenile, and adult Sertoli cells. In addition, GATA-4 mRNA was detected in interstitial cells throughout development. Immunohistochemistry demonstrated GATA-4 protein in both Sertoli and Leydig cells in postnatal animals. The regulation of GATA-4 and GATA-6 expression was explored using established testicular cell lines. Treatment of Leydig tumor cell lines with hCG resulted in a modest, but statistically significant, increase in the steady state level of GATA-4 mRNA, comparable to the previously described effect of FSH on GATA-4 expression in Sertoli cell lines. Gonadotropin or androgen action was not, however, a prerequisite for the basal expression of GATA-4 or GATA-6 in the testis, as their presence in Sertoli and Leydig cells was demonstrated in genetically hypogonadal hpg mice, in rats treated with GnRH receptor antagonist, and in Sertoli cells after chemical abolition of Leydig cells. Cotransfection studies using a GATA-4 expression plasmid and an inhibin alpha promoter/reporter gene construct in Leydig and granulosa tumor cell lines revealed that the inhibin alpha promoter harboring essential GATA-binding sites can be trans-activated by GATA-4. In light of these results, we propose that transcription factors GATA-4 and GATA-6 play differing roles in the maturation and function of testicular somatic cells.

Comparing the thermodynamic stabilities of a related thermophilic and mesophilic enzyme

Several models have been proposed to explain the high temperatures required to denature enzymes from thermophilic organisms; some involve greater maximum thermodynamic stability for the thermophile, and others do not. To test these models, we reversibly melted two analogous protein domains in a two-state manner. E2cd is the isolated catalytic domain of cellulase E2 from the thermophile Thermomonospora fusca. CenAP30 is the analogous domain of the cellulase CenA from the mesophile Cellulomonas fimi. When reversibly denatured in a common buffer, the thermophilic enzyme E2cd had a temperature of melting (Tm) of 72.2 degrees C, a van't Hoff enthalpy of unfolding (DeltaHVH) of 190 kcal/mol, and an entropy of unfolding (DeltaSu) of 0.55 kcal/(mol*K); the mesophilic enzyme CenAP30 had a Tm of 56.4 degrees C, a DeltaHVH of 107 kcal/mol, and a DeltaSu of 0. 32 kcal/(mol*K). The higher DeltaHVH and DeltaSu values for E2cd suggest that its free energy of unfolding (DeltaGu) has a steeper dependence on temperature at the Tm than CenAP30. This result supports models that predict a greater maximum thermodynamic stability for thermophilic enzymes than for their mesophilic counterparts. This was further explored by urea denaturation. Under reducing conditions at 30 degrees C, E2cd had a concentration of melting (Cm) of 5.2 M and a DeltaGu of 11.2 kcal/mol; CenAP30 had a Cm of 2.6 M and a DeltaGu of 4.3 kcal/mol. Under nonreducing conditions, the Cm and DeltaGu of CenAP30 were increased to 4.5 M and 10.8 kcal/mol at 30 degrees C; the Cm for E2cd was increased to at least 7.4 M at 32 degrees C. We were unable to determine a DeltaGu value for E2cd under nonreducing conditions due to problems with reversibility. These data suggest that E2cd attains its greater thermal stability (DeltaTm = 15.8 degrees C) through a greater thermodynamic stability (DeltaDeltaGu = 6.9 kcal/mol) compared to its mesophilic analogue CenAP30.

Fed-batch production of thermomonospora fusca endoglucanase by recombinant streptomyces lividans

The factors affecting the production of a Thermomonospora fusca endoglucanase by a recombinant Streptomyces lividans strain were studied in a fermentor with glucose addition controlled by a pH-stat. The recombinant plasmid was stable for 35 generations with constant endoglucanase productivity. Glucose and peptone were used as the carbon and nitrogen sources. Addition of Tween-80 increased endoglucanase production twofold. A significant decrease in endoglucanase production was observed at low aeration. During fed-batch cultivation, pulse feeding (6 g/L) of a glucose-ammonium sulfate solution was optimal for endoglucanase production. With higher concentrations of glucose (15 g/L), a significant amount of organic acid, including acetic acid, was produced, which inhibited cell growth and endoglucanase production. Under optimum conditions, 1.7 U/mL of endoglucanase were produced. Copyright 1998 John Wiley & Sons, Inc.

Acquired thymic tolerance and experimental allergic encephalomyelitis in the rat. I. Parameters and analysis of possible mechanisms

Intrathymic injection of guinea pig myelin basic protein (MBP) or the immunodominant, encephalitogenic fragment of MPB, 68-86, without otherwise compromising the peripheral lymphocyte pool in adult LEW rats, dramatically inhibits onset of experimental allergic encephalomyelitis (EAE) caused by the usual peripheral inoculation with MBP in complete Freund's adjuvant. This surprising finding demonstrates that interaction of antigen and one or more components of an intact thymus can down-regulate systemic responses by mature T cells already existing in the peripheral lymphocyte pool. How this happens is not known. In studies designed to explore possible mechanisms: (a) adult thymectomized animals remain susceptible to active EAE, thus EAE cannot be attributed solely to recent thymic emigrants that might be inactivated by antigen deposited in the thymus; (b) heterotopic isografts of injected thymic lobes transfer thymic tolerance to secondary recipients, thus the tolerance effect is dominant over an intact, non-treated thymus; (c) T cells from made thymic tolerant but not immunized donors are less effective in causing EAE following adoptive transfer into, and active immunization of, secondary, irradiated recipients; and (d) animals resistant to active EAE as a consequence of thymic tolerance are fully vulnerable to adoptive EAE caused by already activated MBP-specific T cell subpopulations. These results rule out a possible mechanism previously proposed for acquired thymic tolerance, i. e., that potentially pathogenic T cells traffic to the antigen-injected thymus where they are inactivated or eliminated.

Hg2+ removal by genetically engineered Escherichia coli in a hollow fiber bioreactor

Escherichia coli cells engineered to express an Hg2+ transport system and metallothionein accumulated Hg2+ effectively over a concentration range of 0.2-4 mg/L in batch systems. Bioaccumulation was selective against other metal ions and resistant to changes in ambient conditions such as pH, ionic strength, and the presence of common metal chelators or complexing agents (Chen, S.-L.; Wilson, D. B. Appl. Environ. Microbiol. 1997, 63, 2442-2445; Biodegradation 1997, 8, 97-103). Here we report the characterization of the bioaccumulation system based on its kinetics and an isotherm. Bioaccumulation was rapid and followed Michaelis-Menten kinetics. A hollow fiber bioreactor was constructed to retain the genetically engineered cells. The bioreactor was capable of removing and recovering Hg2+ effectively at low concentrations, reducing a 2 mg/L solution to about 5 microgram/L. A mathematical equation that quantitatively described Hg2+ removal by the bioreactor provides a basis for the optimization and extrapolation of the bioreactor. The genetically engineered E. colicells and the bioreactor system have excellent properties for bioremediation of Hg2+-contaminated environments.

Thyroid reoperations: indications and risks

Thyroid reoperations can be technically difficult and associated with an increased risk of complications. To determine the indications for reoperations and the risk of postoperative complications with these procedures, records of 362 patients undergoing thyroidectomy by a single surgeon (R.A.P.) were reviewed. Thirty-two patients had a reoperation. The group consists of 21 women and 11 men with an average age of 55 years (range, 31-79). Twenty-four patients had 1 prior operation, and 8 patients had 2 or more. We performed 4 of the initial operations, and 28 were done by surgeons at other centers. Fourteen reoperations were done for symptomatic multinodular goiter (MNG), and 5 because of a change in the histologic diagnosis from benign to cancerous. The remainder were for further treatment of malignancy. The most common operation was completion thyroidectomy (31). In 3 patients, either unilateral or bilateral modified radical neck exploration was performed. One patient required median sternotomy. One subtotal thyroidectomy was also performed. Recurrent laryngeal nerve injury occurred in 2 patients. It resolved in 1 patient but was permanent in another, who had 3 operations for MNG. One of the 2 patients with preoperative unilateral vocal cord paralysis had return of function after removal of a substernal goiter. The other had a permanent nerve injury from the original surgery. Three patients had postoperative hypocalcemia (calcium <8.0 mg/dL). This resolved in all patients within 1 to 6 months. One patient who had a third operation for MNG had postoperative hemorrhage necessitating tracheostomy for airway control. Another patient developed a seroma that resolved within 2 months. We conclude that reoperations are indicated for both benign and malignant thyroid disease. Because they carry a higher risk of complications, every effort should be made to avoid them by performing definitive initial treatment.

Regulation of biosynthesis of individual cellulases in Thermomonospora fusca

Regulation of the biosynthesis of the six cellulases comprising the cellulolytic system of the thermophilic soil bacterium Thermomonospora fusca ER1 was studied. The levels of the individual enzymes produced on different noninducing and inducing carbon sources were determined. The lowest level of cellulase synthesis (3 nM) was observed with xylose as a carbon source, and the highest level (247 to 1,670 nM for different enzymes) was found in cultures grown on microcrystalline cellulose. Endocellulases and exocellulases showed distinctly different regulation patterns. Differences in the regulation of individual enzymes appear to be determined by the specific structural organization of the upstream regulatory sequences of their genes.

Active-site binding of glycosides by Thermomonospora fusca endocellulase E2

The determination of the high-resolution structure of the Thermomonospora fusca endocellulase E2 catalytic domain makes it ideal for exploring cellulase structure-function relationships. Here we present binding parameters (Kd, DeltaH degrees, and DeltaS degrees) describing the interaction of E2 with 4-methylumbelliferyl glycosides, determined by titrating the quenching of ligand fluorescence in equilibrium binding experiments. Quenched MU(Glc)2/E2 complexes were used as indicators in displacement titrations to measure the binding of natural glycosides and also of a nonhydrolyzable cellotetraose analogue. Binding of MU(Glc)2 and cellotriose were also determined by titration calorimetry. The results show that E2 binds glycosides exclusively in its active-site cleft, with high affinity and specificity. The observed patterns of ligand hydrolysis and the results with MU(Glc)2 as a substrate indicated that ligands bound to E2 with their nonreducing ends in position -2, consistent with the position of cellobiose in the E2cd structure. Polymerase chain reaction (PCR) mutagenesis of the conserved residue Tyr 73 (in E2 binding subsite -1) to Phe and Ser produced enzymes with lower activity but higher binding affinities, indicating that the volume of the subsite -1 binding pocket is crucial for enzyme function. Similarly, MUXylGlc (with its xylosyl unit located in position -1) bound with 100-fold higher affinity than MU(Glc)2. These results are similar to those for the related Trichoderma reesei exocellulase CBH II. The binding data were compared with that previously reported for CBH II and interpreted in terms of the functional differences between endo- and exocellulases.

Factorial optimization of a six-cellulase mixture

A factorial experimental design approach was used to optimize mixtures of six cellulases (five Thermomonospora fusca cellulases and plus/minus Trichoderma reesei CBHI along with beta-glucosidase) so as to maximize the glucose produced from filter paper. Optimized mixture A and mixture B produced glucose at 25 and 8.3 μmol glucose/μmol enzyme/min, respectively, which are 8 and 1.5 times higher than the sum of the activity of the individual cellulases. In both mixtures, the glucose yield depended on the ratio and the cellulases used. Most enzymes showed synergistic interactions that increased the glucose yield. The yield of glucose with the optimum mixtures depended on the total enzyme concentration. Copyright 1998 John Wiley & Sons, Inc.