Mice lacking the Nkx6.2 (Gtx) homeodomain transcription factor develop and reproduce normally

The Nkx homeobox genes are expressed in a variety of developing tissues and have been implicated in controlling tissue patterning and cell differentiation. Expression of Nkx6.2 (Gtx) was previously observed in the embryonic neural tube, testis, and differentiating oligodendrocytes. To investigate the role of Nkx6.2 in the control of cell specification and differentiation, we generated mice with null mutations in Nkx6.2 using the standard gene targeting approach. Null mutant mice were viable and fertile without apparent histological and immunohistochemical changes in the central nervous systems and testis. The absence of detectable phenotypes suggests a redundant function of Nkx6.2 in mouse development.

The proapoptotic protein Bad binds the amphipathic groove of 14-3-3zeta

Through interaction with a multitude of target proteins, 14-3-3 proteins participate in the regulation of diverse cellular processes including apoptosis. These 14-3-3-interacting proteins include a proapoptotic Bcl-2 homolog, Bad (Bcl-2/Bcl-XL-associated death promoter). To understand how 14-3-3 interacts with Bad and modulates its function, we have identified structural elements of 14-3-3 necessary for 14-3-3/Bad association. 14-3-3 contains a conserved amphipathic groove that is required for binding to several of its ligands. We used peptides of known binding specificity as competitors to demonstrate that Bad interacts with 14-3-3zeta via its amphipathic groove. More detailed analysis revealed that several conserved residues in the groove, including Lys-49, Val-176, and Leu-220, were critical for Bad interaction. These results were applied to investigations of the ability of 14-3-3 to prevent Bad-induced cell death. When co-expressed with Akt, wild-type 14-3-3 could reduce the ability of Bad to cause death, however 14-3-3zetaK49E, which cannot bind Bad, failed to inhibit Bad. It seems that the amphipathic groove of 14-3-3 represents a general binding site for multiple ligands, raising issues related to competition of ligands for 14-3-3.

[Effect of wuzi yanzong pill and its disassembled prescription on mitochondrial DNA deletion, respiratory chain complexes and ATP synthesis in aged rats]

OBJECTIVE

To investigate the effect of Wuzi Yanzong Pill (WZYZP) and its disassembled prescription on mitochondrial DNA deletions, respiratory chain complexes and ATP synthesis in aged rats.

METHODS

Animal experiments with polymerase chain reaction (PCR), enzyme kinetics and bioluminescence technique were conducted.

RESULTS

WZYZP and its disassembled prescription of Fructus Lycii and Semen Cuscutae could reduce the mitochondrial DNA deletions and raise the activities of mitochondrial respiratory chain complexes I, IV and adenosine triphosphate (ATP) synthesis in aged rats' brain; Fructus Lycii and Semen Cuscutae could also reduce the mitochondrial DNA deletions in aged rats' heart (P < 0.05, P < 0.01).

CONCLUSION

WZYZP, Fructus Lycii and Semen Cuscutae have protective effect on oxidative damage of mitochondrial DNA in aged rats.

[Alterations in the level of calcitonin gene related peptide and endothelin-1 in the cirrhotic rat heart]

OBJECTIVE

To investigate the role of calcitonin gene related peptide(CGRP) and endothelin-1 (ET-1) in cirrhotic cardiomyopathy (CCM).

METHODS

We measured the level of CGRP and ET-1 in the samples of rat heart collected from 15 liver cirrhosis rats and 15 controls by using radio immunoassay.

RESULTS

The data showed that the levels of CGRP (74.2130 +/- 10.3776 pg/mg protein) and ET-1 level (1.4780 +/- 0.9235 pg/mg protein) were significantly higher in the cirrhotic rat hearts than those in controls (P < 0.05). The increase of ET-1 in the cirrhotic rat hearts was closely associated with the severity of liver cirrhosis (P = 0.004); whereas no significant association was seen between the CGRP concentration and the severity of liver cirrhosis (P = 0.307).

CONCLUSION

We infer that the increasing of CGRP level in the cirrhotic rat heart may be a protective or antagonistic reaction to ET-1 or other pathogenic factors for cardiac dysfunction. The disturbance of the balance between CGRP and ET-1 in the liver cirrhosis rat hearts may contribute to the pathologic process of CCM.

[TGF beta 1 and ET-1 expression in the peripheral blood of patients with cirrhosis]

OBJECTIVE

The aims of this study were to determine 1. the variation of blood TGF beta 1 and ET-1 in patients with liver cirrhosis; 2. the relationship of the blood TGF beta 1 and ET-1 with Child degree of liver function and the severity of esophageal varices.

METHODS

Peripheral blood samples were obtained from 72 patients and 24 normal controls. The blood levels of TGF beta 1 and ET-1 were measured by using a standard bioassay and the radioimmunoassay.

RESULTS

TGF beta 1 level (11.77 +/- 1.32 ng/ml) and ET-1 level (78.37 +/- 17.54 pg/ml) were significantly higher in the patients than those in controls(P < 0.05). The increase of the ET-1 in the patients is closely associated with Child degree of liver function (r = 0.94) and the severity of esophageal varices(r = 0.87). TGF beta 1 concentration is not associated with Child degree of liver function (r = 0.11) and the severity of esophageal varices (r = 0.03).

CONCLUSION

TGF beta 1 and ET-1 may play an important role in the pathophysiologic process of cirrhosis. ET-1 concentration may reflect portal hypertension development.

Supramolecular origins of product selectivity for methanol-to-olefin catalysis on HSAPO-34

Ethylene selectivity in methanol-to-olefin (MTO) catalysis is related to the number of methyl groups on benzene rings trapped in the nanocages of the preferred catalyst HSAPO-34. By correlating the time evolutions of the catalysts' 13C NMR spectra and the volatile product distribution following abrupt cessation of methanol flow, we discovered that (in the absence of other adsorbates) propene is favored by methylbenzenes with four to six methyl groups but ethylene is predominant from those with two or three methyl groups. We substantially increased ethylene selectivity by operating at lower methanol partial pressures or higher temperatures, either of which reduces the steady-state average methyl substitution. As a step toward a kinetic analysis of the MTO reaction on HSAPO-34, we treated each nanocage with a methylbenzene molecule as a supramolecule capable of unimolecular dissociation into ethylene or propene and a less highly substituted methylbenzene. Addition of a water molecule to a nanocage containing a methylbenzene produces a distinct supramolecule with unique properties. Indeed, co-feeding water with methanol significantly increased the average number of methyl groups per ring at steady state relative to identical conditions without additional water, and also increased ethylene selectivity, apparently through transition state shape selectivity.

[Effects of transforming growth factor beta 1 on the expression of integrin beta 3 and the activity of focal adhesion kinase on human vascular endothelial cell]

OBJECTIVE

To observe the effects of transforming growth factors beta 1 (TGF beta 1) on the expression of integrin beta 3 and the activity of focal adhesion kinase (FAK).

METHODS

This study was performed on cultured human endothelial cells (EC) by using cell-ELISA and immunoprecipitation-tyrosine kinase assay respectively.

RESULTS

Under the stimulus of TGF beta 1, there a dose-dependent increase in the expression of integrin beta 3 chain in the surface of EC. And after the cultured EC were treated with 5 ng/ml or 10 ng/ml TGF beta 1 for 6 or 24 hours, the FAK activity in EC increased significantly as compared with the control group (P < 0.05).

CONCLUSION

The expression of integrin beta 3 and the activity of FAK on EC were regulated by TGF beta 1, and this regulation may be important in cell adherence, angiogenesis, and in the pathophysiology of atherosclerosis.

The integrity of the ball-and-socket joint between V and C domains is essential for complete activity of a humanized antibody

AF2 is a high affinity murine Ab possessing potent neutralizing activity against human IFN-gamma. In carrying out the modifications to humanize this Ab, we discovered that an initial version displayed affinity for IFN-gamma that was slightly less than that of AF2, but exhibited IFN-gamma-neutralizing activity that was severely diminished. Characterization via site-directed mutagenesis revealed that the majority of this loss in IFN-gamma-neutralizing activity was due to altering the V(H) framework residue at position 11. V(H) position 11 is distal to the binding surface of the Ab; however, it, along with residues 110 and 112, have been identified as forming the socket of a molecular ball-and-socket joint between the V and C domains of the Ig Fab, which influences the elbow angle between these domains. To determine whether disrupting the structure of this joint was the basis for reduced IFN-gamma-neutralizing capacity, we altered residue 148 of C(H1), which with residue 149 comprises the corresponding ball portion of the joint. Changing this single C(H1) domain residue diminished the ability of the Ab to neutralize IFN-gamma to a level similar to that observed with the V(H) alteration. Thus, an intact ball-and-socket joint between the V and C domains in AF2 is required for potent neutralization of IFN-gamma. These results suggest the importance of the elbow angle between Ig V and C domains in Ab activity, and support the hypothesis that this joint can be an important functional element of Ab structure.

Rearrangement with formamide extrusion in the electrospray mass spectra of aminoacylbenzylamines

Several aminoacylbenzylamines and their analogs were synthesized and analyzed by electrospray ionization mass spectrometry together with high-resolution and tandem mass spectrometric techniques. Fragment ions ([M + H - CH3NO](+)) were observed and attributed to a transfer of the benzyl group to the N-terminal amino group, leading to elimination of formamide. The proposed mechanism is supported by accurate mass measurements, and by experiments on deuterium labeling and variations of functional groups.

Selective expression of Nkx-2.2 transcription factor in chicken oligodendrocyte progenitors and implications for the embryonic origin of oligodendrocytes

Recent studies have demonstrated that oligodendrocytes originate from the ventral region of the developing spinal cord. However, the precise neuroepithelial origin of oligodendrocytes remains controversial, and the transcriptional control of oligodendrocyte lineage specification is largely unknown. Here we present evidence that oligodendrocytes in the embryonic chicken spinal cord can be generated from neuroepithelial cells that express the Nkx-2.2 homeodomain transcription factor. Nkx-2.2 expression is initially confined to a narrow stripe of neuroepithelium flanking the floor plate. Later, Nkx-2.2+ cells migrate ventrally and dorsolaterally into the surrounding gray and white matter regions where they undergo rapid proliferation. Double labeling experiments revealed that Nkx-2.2+ cells coexpress markers specific for oligodendrocyte progenitors, e.g., PDGFRalpha+, O4, and R-mAb antigens. In the brain, the Nkx-2.2 cells are also highly migratory and can generate oligodendrocytes. The persistent expression of the Nkx-2.2 homeodomain transcription factor in the oligodendrocyte lineage suggests its important role in the control of oligodendrocyte development.

[Influence of multiple coats of bonding agent on the bond strength of amalgam bonding]

OBJECTIVE

To evaluate the effect of multiple coats of bond on the bond strength of amalgam bonding.

METHODS

One or two layers of Scotch-bond multi-purpose plus dental adhesive agent were applied on the dental walls of two groups of teeth respectively prior to amalgam condensation. The third group was set for control which only had amalgam filling. After one week, thermocycling, shear bond strength were tested for all specimens with 1195-Instron testing machine. Data were analyzed by SPSS 8.0. The SEM observation were made in other five modals with one or two layers bonding.

RESULTS

The shear strengths of two or one layer bond and control one were 25.77, 20.69 and 13.05 MPa separately. The difference among them was statistical significant (P < 0.01).

CONCLUSIONS

The microlocking was more obvious in specimens of two bonding layers.

Inward potassium channel in guard cells as a target for polyamine regulation of stomatal movements

A number of studies show that environmental stress conditions such as drought, high salt, and air pollutants increase polyamine levels in plant cells. However, little is understood about the physiological function of elevated polyamine levels. We report here that polyamines regulate the voltage-dependent inward K(+) channel in the plasma membrane of guard cells and modulate stomatal aperture, a plant "sensor" to environmental changes. All natural polyamines, including spermidine, spermine, cadaverine, and putrescine, strongly inhibited opening and induced closure of stomata. Whole-cell patch-clamp analysis showed that intracellular application of polyamines inhibited the inward K(+) current across the plasma membrane of guard cells. Single-channel recording analysis indicated that polyamine regulation of the K(+) channel requires unknown cytoplasmic factors. In an effort to identify the target channel at the molecular level, we found that spermidine inhibited the inward K(+) current carried by KAT1 channel that was functionally expressed in a plant cell model. These findings suggest that polyamines target KAT1-like inward K(+) channels in guard cells and modulate stomatal movements, providing a link between stress conditions, polyamine levels, and stomatal regulation.

Overproduction of D-hydantoinase and carbamoylase in a soluble form in Escherichia coli

The production of D-hydantoinase and carbamoylase from Agrobacterium radiobacter NRRL B11291 using T7 and trc promoters, respectively, was found to cause protein aggregates in Escherichia coli. We initiated a systematic study aimed at overproducting these two proteins in a soluble form. As a result, the protein aggregate from carbamoylase overproduction could be alleviated with the aid of GroEL/GroES. In contrast, the production of a high level of D-hydantoinase in an active form can be achieved at low temperature (25 degrees C) or by the coproduction of DnaJ/DnaK. Overall, with such approaches both recombinant proteins gain more than a four-fold increase in enzyme activity. In addition, by fusion with thioredoxin, D-hydantoinase activity can be increased 25% more than the unfused counterpart in the presence of DnaJ/DnaK. These results indicate the success of our approaches to overproducing D-hydantoinase and carbamoylase in a soluble form in E. coli.

Fatal occupational injuries in a new development area in the People's Republic of China

Fatal occupational injuries in a new development region in Shanghai in east China are described. All occupational deaths in the East Pujiang New Area during the period 1991 through 1997 were abstracted from multiple, overlapping source documents. There were 426 deaths and a crude mortality rate of 9.1 per 100,000 workers. The death rate was highest in 1995 (14.6%), when expansion in the area was most rapid. The construction sector accounted for 55% of the deaths, followed by manufacturing (23%) and transport, storage, and telecommunications (11%). Falls, collisions, struck by/against incidents, and electrocutions accounted for 80% of all deaths. Falls led all other causes of deaths (33%) and were particularly prevalent in the construction industry (46% of all deaths in construction). The development of ongoing, comprehensive injury surveillance systems in the People's Republic of China will be essential to target and evaluate injury prevention activities in the future.

Fatal occupational injuries in the construction industry of a new development area in east China, 1991 to 1997

Two hundred thirty-five work-related deaths occurred in the construction industry in a new economic development area in eastern China between 1991 and 1997. These fatalities represented 55% of all occupational deaths. The average annual mortality rate was 51.5 per 100,000 construction workers. Falls were the leading cause of death (46.4%). Falls, collisions, struck by/against something, electrocutions, and excavation cave-ins were the main fatality antecedents, accounting for nearly 93.6% of all fatalities. The most common antecedents for incidents with multiple fatalities were falls, crane-related events, poisoning, and fire. These categories of antecedents were similar to those encountered in the construction industry in the United States. These data suggest that organizations need to focus on these event types when planning their prevention activities. Moreover, improved surveillance systems including computerized databases with narrative descriptions of injury events, antecedent factors, and person-time at-risk data are needed to target interventions more precisely.

14-3-3 proteins: structure, function, and regulation

The 14-3-3 proteins are a family of conserved regulatory molecules expressed in all eukaryotic cells. A striking feature of the 14-3-3 proteins is their ability to bind a multitude of functionally diverse signaling proteins, including kinases, phosphatases, and transmembrane receptors. This plethora of interacting proteins allows 14-3-3 to play important roles in a wide range of vital regulatory processes, such as mitogenic signal transduction, apoptotic cell death, and cell cycle control. In this review, we examine the structural basis for 14-3-3-ligand interactions, proposed functions of 14-3-3 in various signaling pathways, and emerging views of mechanisms that regulate 14-3-3 actions.

Synthesis and antimalarial activity of sixteen dispiro-1,2,4, 5-tetraoxanes: alkyl-substituted 7,8,15,16-tetraoxadispiro[5.2.5. 2]hexadecanes

Sixteen alkyl-substituted dispiro-1,2,4,5-tetraoxanes (7,8,15, 16-tetraoxadispiro[5.2.5.2]hexadecanes) were synthesized to explore dispiro-1,2,4,5-tetraoxane SAR and to identify tetraoxanes with better oral antimalarial activity than prototype tetraoxane 1 (WR 148999). The tetraoxanes were prepared either by peroxidation of the corresponding cyclohexanone derivatives in H(2)SO(4)/CH(3)CN or by ozonolysis of the corresponding cyclohexanone methyl oximes. Those tetraoxanes with alkyl substituents at the 1 and 10 positions were formed as single stereoisomers, whereas the five tetraoxanes formed without the stereochemical control provided by alkyl groups at the 1 and 10 positions were isolated as mixtures of diastereomers. Three of the sixteen tetraoxanes were inactive (IC(50)'s > 1000 nM), but five (2, 6, 10, 11, 12) had IC(50)'s between 10 and 30 nM against the chloroquine-sensitive D6 and chloroquine-resistant W2 clones of Plasmodium falciparum compared to corresponding IC(50)'s of 55 and 32 nM for 1 and 8.4 and 7.3 nM for artemisinin. We suggest that tetraoxanes 13, 16, and 17 were inactive and tetraoxanes 4 and 7 were weakly active due to steric effects preventing or hindering peroxide bond access to parasite heme. Tetraoxanes 1, 10, 11, and 14, along with artemisinin and arteether as controls, were administered po b.i.d. (128 mg/kg/day) to P. berghei-infected mice on days 3, 4, and 5 post-infection. At this dose, tetraoxanes 10, 11, and 14 cured between 40% and 60% of the infected animals. In comparison, artemisinin and tetraoxane 1 produced no cures, whereas arteether cured 100% of the infected animals. There was no apparent relationship between tetraoxane structure and in vitro neurotoxicity, nor was there any correlation between antimalarial activity and neurotoxicity for these seventeen tetraoxanes.

Agonist-like activity of antibodies to angiotensin II receptor subtype 1 (AT1) from rats immunized with AT1 receptor peptide

In the present study, rats were immunized with angiotensin II receptor subtype 1 (AT1) receptor peptides for 3 months to see if the immunization produced specific anti-AT1 receptor antibodies and if continuous stimulation for 3 months affected blood pressure or induced morphological changes in the organs containing AT1 receptors. Our results showed that there were constant high levels of circulating antibodies throughout the study period in all rats of the immunized group, but not in the control rats, and that there were almost no significant cross-reactions of antisera with AT2 receptor peptide and alpha1 adrenoceptor peptide, except in four rats, which showed low cross-reactions with alpha1 adrenoceptor and AT2 receptor peptides. When an affinity-purified anti-AT1 receptor antibody was used, it specifically displayed the AT1-stimulatory positive chronotropic effect and also localized AT1 receptors. However, in the immunized group, saturation binding of AT1 in homogenates from kidneys showed no difference either in maximal binding sites (Bmax) or in antagonist affinity (Kd). No difference in mRNA of AT1a was found in either kidney or heart, and no morphological changes in the organs were observed, as compared with the control group. Furthermore, immunization did not cause hypertension. In conclusion, the synthetic peptide corresponding to the second extra-cellular loop of the human AT1 receptor was able to produce highly specific and functionally active anti-AT1 receptor antibodies, but unable to induce pathological structural changes or hypertension.

A gene-enriched BAC library for cloning large allele-specific fragments from maize: isolation of a 240-kb contig of the bronze region

A generic bacterial artificial chromosome (BAC) library from a complex plant genome like maize may not be suitable for some types of genomic analysis, for example, for establishing correlations between the genetic and the physical organization of a given chromosome region. Previously, we carried out extensive genetic analysis of the bronze (Bz) region in Zea mays using a W22 inbred line carrying the Bz-McC allele; however, BAC libraries of that line are neither available nor under construction. Here, we report the isolation of large, adjacent BAC clones of this region from a partial BAC library of W22. We developed a BAC vector suitable for cloning NotI fragments and used it to clone size-fractionated genomic DNA that had been cut to completion with the methylation-sensitive, rare-cutting enzyme NotI. This strategy resulted in a very significant enrichment of large genic DNA. From a library of about 20,000 BACs, containing just two-thirds of a maize genome, we isolated 16 BAC clones of the 110-kb distal Bz fragment and 10 BAC clones of the 130-kb proximal Bz fragment. This recovery means that our strategy resulted in a 15- to 24-fold enrichment of specific sequences. The order of the BAC clones in the 240-kb contig, predetermined from an internal NotI site in the Bz-McC allele was confirmed by hybridization with sequences from sites previously mapped proximal and distal to Bz and by sequencing. To show the general utility of our approach and the value of our partial BAC library, we also isolated BAC clones of other sequences, such as tub4 and the complex R-r allele, contained in the same size fraction of DNA. This is the first report of the use of a BAC vector to clone allele-specific large DNA fragments from a plant with a large genome, circumventing the need to construct a complete BAC library.

Modulation of 14-3-3 protein interactions with target polypeptides by physical and metabolic effectors

The proteins commonly referred to as 14-3-3s have recently come to prominence in the study of protein:protein interactions, having been shown to act as allosteric or steric regulators and possibly scaffolds. The binding of 14-3-3 proteins to the regulatory phosphorylation site of nitrate reductase (NR) was studied in real-time by surface plasmon resonance, using primarily an immobilized synthetic phosphopeptide based on spinach NR-Ser543. Both plant and yeast 14-3-3 proteins were shown to bind the immobilized peptide ligand in a Mg2+-stimulated manner. Stimulation resulted from a reduction in KD and an increase in steady-state binding level (Req). As shown previously for plant 14-3-3s, fluorescent probes also indicated that yeast BMH2 interacted directly with cations, which bind and affect surface hydrophobicity. Binding of 14-3-3s to the phosphopeptide ligand occurred in the absence of divalent cations when the pH was reduced below neutral, and the basis for enhanced binding was a reduction in K(D). At pH 7.5 (+Mg2+), AMP inhibited binding of plant 14-3-3s to the NR based peptide ligand. The binding of AMP to 14-3-3s was directly demonstrated by equilibrium dialysis (plant), and from the observation that recombinant plant 14-3-3s have a low, but detectable, AMP phosphatase activity.

What is the material base of acupuncture? The nerves!

Acupuncture is a traditional Chinese medical method which has been used in the treatment of patients for thousands of years. It is rejected by modern science for lack of solid material background. In recent years, more and more laboratory proof has accumulated that acupuncture can change the charge and potential of neurons, the concentrations of K(+), Na(+), Ca(++) and the content of neuro-transmitters such as aspartate, and taurine and the quantities of neuro-peptides such as beta-endorphin and leu-enkephalin. All these phenomena are directly related to nerve cells. Now the lengthy discussion may conclude that nerve cells and the central nervous system are the real material base of acupuncture.

[Study on therapeutic mechanism of anti-rheumatism action of herba siegesbeckiae]

OBJECTIVE

To explore the mechanism of anti-rheumatism action of the active fraction of Herba Siegesbeckiae (AFHS).

METHODS

Adjuvant arthritis model of rat was made to observe the effect of AFHS on lymphocyte proliferation, interluekin-1 (IL-1) and IL-2 activity, pathologic section of ankle joint, and analgesic effect of AFHS in model rat.

RESULTS

AFHS could reduce the inflammatory pathologic response of ankle joint, it functions well as analgesics, the analgesic rate being 65%, AFHS could also improve T-lymphocyte proliferation, improve IL-2 activity and inhibit IL-1 activity, as compared with the control group, the difference was significant (P < 0.01).

CONCLUSION

Through regulating the immune function of organism, AFHS could improve the local pathologic response so as to antagonise against rheumatism, therefore, it is a good anti-rheumatism herbal medicine.

Formation of functional heterologous complexes using subunits from the picromycin, erythromycin and oleandomycin polyketide synthases

BACKGROUND

Recently developed tools for the genetic manipulation of modular polyketide synthases (PKSs) have advanced the development of combinatorial biosynthesis technologies for drug discovery. Although many of the current techniques involve engineering individual domains or modules of the PKS, few experiments have addressed the ability to combine entire protein subunits from different modular PKSs to create hybrid polyketide pathways. We investigated this possibility by in vivo assembly of heterologous PKS complexes using natural and altered subunits from related macrolide PKSs.

RESULTS

The pikAI and pikAII genes encoding subunits 1 and 2 (modules 1-4) of the picromycin PKS (PikPKS) and the eryAIII gene encoding subunit 3 (modules 5-6) of the 6-deoxyerythronolide B synthase (DEBS) were cloned in two compatible Streptomyces expression vectors. A strain of Streptomyces lividans co-transformed with the two vectors produced the hybrid macrolactone 3-hydroxynarbonolide. Co-expression of the same pik genes with the gene for subunit 3 of the oleandomycin PKS (OlePKS) was also successful. A series of hybrid polyketide pathways was then constructed by combining PikPKS subunits 1 and 2 with modified DEBS3 subunits containing engineered domains in modules 5 or 6. We also report the effect of junction location in a set of DEBS-PikPKS fusions.

CONCLUSIONS

We show that natural as well as engineered protein subunits from heterologous modular PKSs can be functionally assembled to create hybrid polyketide pathways. This work represents a new strategy that complements earlier domain engineering approaches for combinatorial biosynthesis in which complete modules or PKS protein subunits, in addition to individual enzymatic domains, are used as building blocks for PKS engineering.

Identification of self-assembly products from N-phosphoamino acids by electrospray ionization mass spectrometry

The self-assembly products of N-(O,O'-diisopropyl)-L-alpha-amino acids in aqueous media, N-(O,O'-diisopropyl)phosphoryl dipeptides and tripeptides, were identified by electrospray ionization mass spectrometry. A stepwise fragmentation of the [M + H](+) ions from the C-terminus of N-phosphopeptides was observed. Copyright 2000 John Wiley & Sons, Ltd.

Electrospray ionization mass spectra of amino acid phosphoramidates of adenosine

Amino acid phosphoramidates of adenosine were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated. In the positive ion mass spectra abundant characteristic fragment ions appeared, and many complementary ions were found. In the negative ion mass spectra only a few fragment ions were observed, and most of them contained phosphoryl groups. The results show that ESI-MS is a useful tool for structural determination of amino acid phosphoramidates of nucleosides.

The association between health-related behaviours and the risk of divorce in the USA

This study investigates the link between health-related variables and risks of divorce. The findings indicate that physical characteristics associated with poor health--namely, obesity and short stature--are not significantly related to risks of marital dissolution for either men or women. On the other hand, risk-taking behaviours--such as smoking and drug use--are strongly related to higher risks of divorce for both sexes. Overall, the results emphasize the need to accommodate health-related variables in the dominant economic and social psychological theories of marital dissolution.

Structure-based design of selective inhibitors of dihydrofolate reductase: synthesis and antiparasitic activity of 2, 4-diaminopteridine analogues with a bridged diarylamine side chain

As part of a larger search for potent as well as selective inhibitors of dihydrofolate reductase (DHFR) enzymes from opportunistic pathogens found in patients with AIDS and other immune disorders, N-[(2,4-diaminopteridin-6-yl)methyl]dibenz[b,f]azepine (4a) and the corresponding dihydrodibenz[b,f]azepine, dihydroacridine, phenoxazine, phenothiazine, carbazole, and diphenylamine analogues were synthesized from 2, 4-diamino-6-(bromomethyl)pteridine in 50-75% yield by reaction with the sodium salts of the amines in dry tetrahydrofuran at room temperature. The products were tested for the ability to inhibit DHFR from Pneumocystis carinii (pcDHFR), Toxoplasma gondii (tgDHFR), Mycobacterium avium (maDHFR), and rat liver (rlDHFR). The member of the series with the best combination of potency and species selectivity was 4a, with IC(50) values against the four enzymes of 0. 21, 0.043, 0.012, and 4.4 microM, respectively. The dihydroacridine, phenothiazine, and carbazole analogues were also potent, but nonselective. Of the compounds tested, 4a was the only one to successfully combine the potency of trimetrexate with the selectivity of trimethoprim. Molecular docking simulations using published 3D structural coordinates for the crystalline ternary complexes of pcDHFR and hDHFR suggested a possible structural interpretation for the binding selectivity of 4a and the lack of selectivity of the other compounds. According to this model, 4a is selective because of a unique propensity of the seven-membered ring in the dibenz[b,f]azepine moiety to adopt a puckered orientation that allows it to fit more comfortably into the active site of the P. carinii enzyme than into the active site of the human enzyme. Compound 4a was also evaluated for the ability to be taken up into, and retard the growth of, P. carinii and T. gondii in culture. The IC(50) of 4a against P. carinii trophozoites after 7 days of continuous drug treatment was 1.9 microM as compared with previously observed IC(50) values of >340 microM for trimethoprim and 0.27 microM for trimetrexate. In an assay involving [(3)H]uracil incorporation into the nuclear DNA of T. gondii tachyzoites as the surrogate endpoint for growth, the IC(50) of 4a after 5 h of drug exposure was 0.077 microM. The favorable combination of potency and enzyme selectivity shown by 4a suggests that this novel structure may be an interesting lead for structure-activity optimization.

One-step production of D-p-hydroxyphenylglycine by recombinant Escherichia coli strains

The gene encoding D-hydantoinase from Agrobacterium radiobacter NRRL B11291 was successfully cloned by use of polymerase chain reaction. A positive clone was scored, and its nucleotide sequence was further analyzed. The analysis by deleting various lengths of nucleotides from the amino terminus of the open reading frame revealed the putative regions for promoter and RBS site. By highly expressing both D-hydantoinase and carbamoylase, recombinant Escherichia coli strains were able to convert DL-hydroxyphenyl hydantoin (DL-HPH) to D-p-hydroxyphenylglycine (D-HPG) with a conversion yield of 97%, accounting for productivity 5 times higher than that obtained by A. radiobacter NRRL B11291. Immobilizing the recombinant cells with kappa-carrageenan could also achieve a conversion of 93%, while A. radiobacter NRRL B11291 attained 20% within the same period of reaction time. These results illustrate the feasibility in employing recombinant E. coli to accomplish one-step conversion of DL-HPH to D-HPG. In the process of improving D-HPG production, D-hydantoinase activity was increased 2.57-fold but carbamoylase activity remained constant, which resulted in only a 30% increase in the reaction rate. It suggests that carbamoylase is the step setting the pace of the reaction. Since the reaction substrate is highly insoluble, achieving sufficient agitation appears to be an important issue in this heterogeneous system. This view is further supported by the study on repeated use of cells, which shows that to reach a conversion of more than 90% free cells can be recycled six times, whereas immobilized cells can be used only twice. In conclusion, the poor reusability of immobilized cells is due to the fouling on the gel surface.

Analysis of 541 cases of occupational acute chemical injuries in a large petrochemical company in China

The authors carried out a descriptive analysis of acute chemical intoxication in a large petrochemical corporation with 38,000 employees, located in a suburban district of Shanghai, China, to determine the chemicals involved and the primary causes of the incidents. Between 1977 and 1997, 350 cases of acute chemical-intoxication were recorded, resulting in a total of 541 workers with symptoms. Of these, 483 were male and 58, female, with over half the victims under 30 years old. Two hundred and seventy-five cases were serious enough to necessitate hospital admission. There were 266 cases of chemical irritation or inhalation responses (49.2%), 215 cases of mild chemical poisoning (39.7%), 31 cases of moderate poisoning (5.7%), and 29 cases resulting in critical injury (5.4%), including eight deaths (1.5%). The main causes of injury reported by patients were lack of training about safety (63%) and equipment failure (23%). The chemicals involved were asphyxiating gases (302 cases; 55.8%), irritating gases (111 cases; 20.5%), and other toxins. Intervention strategies for the prevention of acute chemical exposures were suggested to the corporation.

[Relationships of angiotensinogen gene M235T variant with diabetic nephropathy in Chinese type 2 diabetes mellitus]

OBJECTIVE

To investigate whether angiotensinogen(AGT) gene M235T variant is associated with type 2 diabetes mellitus without nephropathy (DM) and/or diabetic nephropathy (DN) in Chinese type 2 diabetes.

METHODS

AGT genotypes of 84 cases with DM, 96 with DN and 98 controls were determined by polymerase chain reaction (PCR) amplification and restriction fragment length polymorphism analysis of the region of the variant.

RESULTS

Increased frequencies of T allele (0.82) and TT genotype (0.70) were observed in 96 subjects with DN, compared with those observed in 98 control subjects (0.63 and 0. 43 respectively, P = 0.003, P = 0.0004). The odds ratio associated with TT genotype was 3.47 (95% CI 1.51-7.94, P = 0.0033) for DN in analysis adjusted for several DN risk factors. There was no difference in allele distribution between 84 DM patients and the controls.

CONCLUSION

TT genotype of the AGT gene might be an independent risk factor of diabetic nephropathy in Chinese patients with type 2 diabetes mellitus.

Isolation of high-affinity peptide antagonists of 14-3-3 proteins by phage display

The 14-3-3 proteins interact with diverse cellular molecules involved in various signal transduction pathways controlling cell proliferation, transformation, and apoptosis. To aid our investigation of the biological function of 14-3-3 proteins, we have set out to identify high-affinity antagonists. By screening phage display libraries, we have identified a set of peptides which bind 14-3-3 proteins. One of these peptides, termed R18, exhibited a high affinity for different isoforms of 14-3-3 with estimated K(D) values of 7-9 x 10(-)(8) M. Recognition of multiple isoforms of 14-3-3 suggests the targeting of R18 to a structure that is common among 14-3-3 proteins, such as the conserved ligand-binding groove. Indeed, mutations that alter critical residues in the ligand-binding site of 14-3-3 drastically decreased the level of 14-3-3-R18 association. R18 efficiently blocked the binding of 14-3-3 to the kinase Raf-1, a physiological ligand of 14-3-3, and effectively abolished the protective role of 14-3-3 against phosphatase-induced inactivation of Raf-1. The cocrystal structure of R18 in complex with 14-3-3zeta revealed the occupancy of the general binding groove of 14-3-3zeta by R18, explaining the potent inhibitory effect of R18 on 14-3-3-ligand interactions. Such a well-defined peptide will be an effective tool for probing the role of 14-3-3 in various signaling pathways, and may lead to the development of 14-3-3 antagonists with pharmacological applications.

Residues of 14-3-3 zeta required for activation of exoenzyme S of Pseudomonas aeruginosa

Exoenzyme S (ExoS) is a mono-ADP-ribosyltransferase secreted by the opportunistic pathogen Pseudomonas aeruginosa. ExoS requires a eukaryotic factor, the 14-3-3 protein, for enzymatic activity. Here, two aspects of the activation of the ADP-ribosyltransferase activity of ExoS by 14-3-3 proteins are examined. Initial studies showed that several isoforms of 14-3-3, including beta, zeta, eta, sigma, and tau, activated ExoS with similar efficiency. This implicates a conserved structure in 14-3-3 that contributes to the interaction between 14-3-3 and ExoS. One candidate structure is the conserved amphipathic groove that mediates the 14-3-3/Raf-1 interaction. The next series of experiments examined the role of individual amino acids of the amphipathic groove of 14-3-3 zeta in ExoS activation and showed that ExoS activation required the basic residues lining the amphipathic groove of 14-3-3 zeta without extensive involvement of the hydrophobic residues. Strikingly, mutations of Val-176 of 14-3-3 zeta that disrupted its interaction with Raf-1 did not affect the binding and activation of ExoS by 14-3-3. Thus, ExoS selectively employs residues in the Raf-binding groove for its association with 14-3-3 proteins.

Multiubiquitin chain binding subunit MCB1 (RPN10) of the 26S proteasome is essential for developmental progression in Physcomitrella patens

The 26S proteasome, a multisubunit complex, is the primary protease of the ubiquitin-mediated proteolytic system in eukaryotes. We have recently characterized MCB1 (RPN10), a subunit of the 26S complex that has affinity for multiubiquitin chains in vitro and as a result may function as a receptor for ubiquitinated substrates. To define the role of MCB1 further, we analyzed its function in Physcomitrella patens by generating MCB1 gene disruptions using homologous recombination. PpMCB1, which is 50 to 75% similar to orthologs from other eukaryotes, is present in the 26S proteasome complex and has a similar affinity for multiubiquitin chains, using a conserved hydrophobic domain within the C-terminal half of the polypeptide. Unlike yeast Deltamcb1 strains, which grow normally, P. patens Deltamcb1 strains are viable but are under developmental arrest, generating abnormal caulonema that are unable to form buds and gametophores. Treatment with auxin and cytokinin restored bud formation and subsequent partial development of gametophores. Complementation of a Deltamcb1 strain with mutated versions of PpMCB1 revealed that the multiubiquitin chain binding site is not essential for the wild-type phenotype. These results show that MCB1 has an important function in the 26S proteasome of higher order eukaryotes in addition to its ability to bind multiubiquitin chains, and they provide further support for a role of the ubiquitin/26S proteasome proteolytic pathway in plant developmental processes triggered by hormones.

Elucidating the mechanism of chain termination switching in the picromycin/methymycin polyketide synthase

BACKGROUND

A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates.

RESULTS

The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones.

CONCLUSIONS

These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.

Suppression of apoptosis signal-regulating kinase 1-induced cell death by 14-3-3 proteins

Apoptosis signal-regulating kinase 1 (ASK1) is a pivotal component of a signaling pathway induced by many death stimuli, including tumor necrosis factor alpha, Fas, and the anticancer drugs cisplatin and paclitaxel. Here we report that ASK1 proapoptotic activity is antagonized by association with 14-3-3 proteins. We found that ASK1 specifically bound 14-3-3 proteins via a site involving Ser-967 of ASK1. Interestingly, overexpression of 14-3-3 in HeLa cells blocked ASK1-induced apoptosis whereas disruption of the ASK1/14-3-3 interaction dramatically accelerated ASK1-induced cell death. Targeting of ASK1 by a 14-3-3-mediated survival pathway may provide a novel mechanism for the suppression of apoptosis.

The barriers to bluetongue virus infection, dissemination and transmission in the vector, Culicoides variipennis (Diptera: Ceratopogonidae)

Transmission of bluetongue virus (BTV) by a vector species of Culicoides was studied using immunohistochemistry, virus titration and in vitro transmission tests. Adult female C. variipennis were used from two colonies that are either "transmission competent" or "transmission refractory" after oral infection with BTV. Intrathoracic (i.t.) injection of BTV into the haemocoel always resulted in a fully disseminated infection and transmission of virus in saliva. However, after ingestion of an infectious blood meal, only 30% (approximately) of midges from either colony became persistently infected. Although none of the orally infected insects from the "refractory" colony were able to transmit virus, 12% of those from the "competent" colony (containing > or = 10(3.0)TCID50 of virus/midge) did transmit BTV in their saliva. The most important barriers to BTV transmission in Culicoides vector species appeared to be a mesenteron infection barrier (MIB), which controls initial establishment of persistent infection, a mesenteron escape barrier (MEB) which can restrict virus to gut cells and a dissemination barrier (DB) which can prevent virus which enters the haemocoel from infecting secondary target organs. Culicoides variipennis do not appear to present either a salivary gland infection barrier (SGIB), or a salivary gland escape barrier (SGEB) to BTV.

Comparison between supercritical carbon dioxide extraction and aqueous surfactant washing of an oily machining waste

Mathematical models are developed to compare aqueous surfactant washing to supercritical carbon dioxide (SCCO2) extraction. These two cleaning processes are potentially competitive technologies which can be used to remove oily contaminants from a solid waste. In both processes, the cleaning efficiency for a batch of waste is evaluated by quantifying the residual oil content in the treated sample. A mass transfer model is used to simulate a semi-continuous washing process, and the experimental data, obtained in a batch operation, are used to estimate the equilibrium parameters in the model. For SCCO2 extraction, a linear desorption model is used to describe the supercritical desorption of oil from the solid phase into the CO2 phase and the simulated results agreed very well with the experimental data. The oil removal in aqueous surfactant washing is viewed to be controlled primarily by the diffusional transport of oil from the interiors of the waste elements to the surface, thus, it can be significantly affected by the size of the particles. A pre-cleaning pulverization is then recommended to improve the cleaning efficiency without increasing any other operation costs. In SCCO2 extraction, the desorption of oil from the solid waste is the controlling step and consequently, the solvent flow rate has no influence on oil removal. Our theoretical studies show that the difference between the cleaning efficiencies of these two technologies is not significant, with the oil concentration in the washing products approximately 5% lower than that in the extraction products.

A study on oxidative stress in lead-exposed workers

To explore the possible oxidative stress induced by lead, heparinized whole blood and urine of 66 secondary smelter lead workers (46 for Comet assay) and 28 controls were collected. The concentrations of blood lead (BPb) and urinary lead (UPb) and alpha-aminolevulinic acid (alpha-ALA), indices of lead exposure level of the body, were determined. Malondialdehyde (MDA) concentrations and superoxide dismutase (SOD) activity of plasma were also measured. Single-cell gel (SCG, Comet assay) was used to measure the DNA damage of peripheral blood cells. There was a positive correlation between the presence of Pb in blood and significant increases in MDA levels and SOD activity. Alcohol consumption and smoking with increased exposure to Pb was associated with enhanced DNA damage. A positive correlation was found between MDA and DNA damage.

Structural and functional analysis of the six regulatory particle triple-A ATPase subunits from the Arabidopsis 26S proteasome

The 26S proteasome is a multi-subunit ATP-dependent protease responsible for degrading most short-lived intracellular proteins targeted for breakdown by ubiquitin conjugation. The complex is composed of two relatively stable subparticles, the 20S proteasome, a hollow cylindrical structure which contains the proteolytic active sites in its lumen, and the 19S regulatory particle (RP) which binds to either end of the cylinder and provides the ATP-dependence and the specificity for ubiquitinated proteins. Among the approximately 18 subunits of the RP from yeast and animals are a set of six proteins, designated RPT1-6 for regulatory particle triple-A ATPase, that form a distinct family within the AAA superfamily. Presumably, these subunits use ATP hydrolysis to help assemble the 26S holocomplex, recognize and unfold appropriate substrates, and/or translocate the substrates to the 20S complex for degradation. Here, we describe the RPT gene family from Arabidopsis thaliana. From a collection of cDNAs and genomic sequences, a family of genes encoding all six of the RPT subunits was identified with significant amino acid sequence similarity to their yeast and animal counterparts. Five of the six RPT sub- units are encoded by two genes; the exception being RPT3 which is encoded by a single gene. mRNA for each of the six proteins is present in all tissue types examined. Five of the subunits (RPT1 and 3-6) complemented yeast mutants missing their respective orthologs, indicating that the yeast and Arabidopsis proteins are functionally equivalent. Taken together, these results demonstrate that the RP, like the 20S proteasome, is functionally and structurally conserved among eukaryotes and indicate that the plant RPT subunits, like their yeast counterparts, have non-redundant functions.

Xylene-induced effects on brain neurotransmitters, behavior and fos protein in rats

Male Sprague-Dawley rats administered xylene intraperitoneally on alternate days at a dose of 125 or 250 mg/kg for 30 days exhibited no marked changes in locomotor activity, learning and memory capacity. However in rats given xylene on alternate day at a dose of 500 mg/kg for 30 days, a significant decrease in locomotor activity, deficits in learning ability and memory loss were detected. These xylene-induced behavioral changes were associated with a decrease in beta-endorphin and leuenkaphlin concentrations in the pons-medulla. On the contrary, xylene at a dose of 500 mg/kg increased the beta-endorphin level in caudate and c-fos expression in hippocampus. These data suggest that the xylene-induced behavioral alterations might be associated with the expression of Fos protein in the hippocampus.

Treatment of atrophic cholecystitis by regulating the spleen--a report of 50 cases

Fifty cases of atrophic cholecystitis were treated by regulating of the spleen. Of them, 21 were cured, 18 remarkably effective, and 7 effective. The overall effective rate was 92.0%. As compared with the results of ultrasonography B performed before and after treatment, it was shown that both the longitudinal and transverse inner diameters of the gallbladder increased evidently, and the condition of atrophy improved remarkably after treatment.

Interaction of 14-3-3 with a nonphosphorylated protein ligand, exoenzyme S of Pseudomonas aeruginosa

The 14-3-3 proteins are a family of conserved, dimeric proteins that interact with a diverse set of ligands, including molecules involved in cell cycle regulation and apoptosis. It is well-established that 14-3-3 binds to many ligands through phosphoserine motifs. Here we characterize the interaction of 14-3-3 with a nonphosphorylated protein ligand, the ADP-ribosyltransferase Exoenzyme S (ExoS) from Pseudomonas aeruginosa. By using affinity chromatography and surface plasmon resonance, we show that the zeta isoform of 14-3-3 (14-3-3zeta) can directly bind a catalytically active fragment of ExoS in vitro. The interaction between ExoS and 14-3-3zeta is of high affinity, with an equilibrium dissociation constant of 7 nM. ExoS lacks any known 14-3-3 binding motif, but to address the possibility that 14-3-3 binds a noncanonical phosphoserine site, we assayed ExoS for protein-bound phosphate by using mass spectrometry. No detectable phosphoproteins were found. A phosphopeptide ligand of 14-3-3, pS-Raf-259, was capable of inhibiting the binding of 14-3-3 to ExoS, suggesting that phosphorylated and nonphosphorylated ligands may share a common binding site, the conserved amphipathic groove. It is conceivable that 14-3-3 proteins may bind both phosphoserine and nonphosphoserine ligands in cells, possibly allowing kinase-dependent as well as kinase-independent regulation of 14-3-3 binding.

Structure and functional analysis of the 26S proteasome subunits from plants

As initial steps to define how the 26S proteasome degrades ubiquitinated proteins in plants, we have characterized many of the subunits that comprise the proteolytic complex from Arabidopsis thaliana. A set of 23 Arabidopsis genes encoding the full complement of core particle (CP) subunits and a collection encoding 12 out of 18 known eukaryotic regulatory particle (RP) subunits, including six AAA-ATPase subunits, were identified. Several of these 26S proteasome genes could complement yeast strains missing the corresponding orthologs. Using this ability of plant subunits to functionally replace yeast counterparts, a parallel structure/function analysis was performed with the RP subunit RPN 10/MCB1, a putative receptor for ubiquitin conjugates. RPN10 is not essential for yeast viability but is required for amino acid analog tolerance and degradation of proteins via the ubiquitin-fusion degradation pathway, a subpathway within the ubiquitin system. Surprisingly, we found that the C-terminal motif required for conjugate recognition by RPN10 is not essential for in vivo functions. Instead, a domain near the N-terminus is required. We have begun to exploit the moss Physcomitrella patens as a model to characterize the plant 26S proteasome using reverse genetics. By homologous recombination, we have successfully disrupted the RPN10 gene. Unlike yeast rpn10delta strains which grow normally, Physcomitrella rpn10delta strains are developmentally arrested, being unable to initiate gametophorogenesis. Further analysis of these mutants revealed that RPN10 is likely required for a developmental program triggered by plant hormones.

Functional analysis of the proteasome regulatory particle

We have developed S. cerevisiae as a model system for mechanistic studies of the 26S proteasome. The subunits of the yeast 19S complex, or regulatory particle (RP), have been defined, and are closely related to those of mammalian proteasomes. The multiubiquitin chain binding subunit (S5a/Mcb1/Rpn10) was found, surprisingly, to be nonessential for the degradation of a variety of ubiquitin-protein conjugates in vivo. Biochemical studies of proteasomes from deltarpn10 mutants revealed the existence of two structural subassemblies within the RP, the lid and the base. The lid and the base are both composed of 8 subunits. By electron microscopy, the base and the lid correspond to the proximal and distal masses of the RP, respectively. The base is sufficient to activate the 20S core particle for degradation of peptides, but the lid is required for ubiquitin-dependent degradation. The lid subunits share sequence motifs with components of the COP9/signalosome complex, suggesting that these functionally diverse particles have a common evolutionary ancestry. Analysis of equivalent point mutations in the six ATPases of the base indicate that they have well-differentiated functions. In particular, mutations in one ATPase gene, RPT2, result in an unexpected defect in peptide hydrolysis by the core particle. One interpretation of this result is that Rpt2 participates in gating of the channel through which substrates enter the core particle.

Multiple genetic modifications of the erythromycin polyketide synthase to produce a library of novel "unnatural" natural products

The structures of complex polyketide natural products, such as erythromycin, are programmed by multifunctional polyketide synthases (PKSs) that contain modular arrangements of functional domains. The colinearity between the activities of modular PKS domains and structure of the polyketide product portends the generation of novel organic compounds-"unnatural" natural products-by genetic manipulation. We have engineered the erythromycin polyketide synthase genes to effect combinatorial alterations of catalytic activities in the biosynthetic pathway, generating a library of >50 macrolides that would be impractical to produce by chemical methods. The library includes examples of analogs with one, two, and three altered carbon centers of the polyketide products. The manipulation of multiple biosynthetic steps in a PKS is an important milestone toward the goal of producing large libraries of unnatural natural products for biological and pharmaceutical applications.

[Gas chromatography/mass spectrometry analysis for determination of methyl alpha-(6-methoxyl-2-naphthyl) propionate from carbonylation]

alpha-(6-Methoxyl-2-naphthyl) ethanol can be carbonylated to form methyl-alpha-(6-methoxyl-2-naphthyl)propionate catalyzed by a catalyst in the pressnce of methanol. High efficiency capillary gas chromatography and GC/MS technique were used for determining products which were obtained from the carbonylation. An OV-101 fused silica capillary column (25 m x 0.2 mm i.d.) and a flame ionization detector (FID) were employed in the GC analysis. The column temperature was kept at 250 degrees C. Mass spectra were obtained by electron impact at 70 eV. The structures of four compounds were identified. The major product is methyl-alpha-(6-methoxy-2-naphthyl) propionate, and the two by-products are 2-vinyl-6-methoxynaphthalene and 1-methoxy-(6'-methoxy-2'-naphthyl)ethanol.

Contraceptive failure rates: new estimates from the 1995 National Survey of Family Growth

CONTEXT

Unintended pregnancy remains a major public health concern in the United States. Information on pregnancy rates among contraceptive users is needed to guide medical professionals' recommendations and individuals' choices of contraceptive methods.

METHODS

Data were taken from the 1995 National Survey of Family Growth (NSFG) and the 1994-1995 Abortion Patient Survey (APS). Hazards models were used to estimate method-specific contraceptive failure rates during the first six months and during the first year of contraceptive use for all U.S. women. In addition, rates were corrected to take into account the underreporting of induced abortion in the NSFG. Corrected 12-month failure rates were also estimated for subgroups of women by age, union status, poverty level, race or ethnicity, and religion.

RESULTS

When contraceptive methods are ranked by effectiveness over the first 12 months of use (corrected for abortion underreporting), the implant and injectables have the lowest failure rates (2-3%), followed by the pill (8%), the diaphragm and the cervical cap (12%), the male condom (14%), periodic abstinence (21%), withdrawal (24%) and spermicides (26%). In general, failure rates are highest among cohabiting and other unmarried women, among those with an annual family income below 200% of the federal poverty level, among black and Hispanic women, among adolescents and among women in their 20s. For example, adolescent women who are not married but are cohabiting experience a failure rate of about 31% in the first year of contraceptive use, while the 12-month failure rate among married women aged 30 and older is only 7%. Black women have a contraceptive failure rate of about 19%, and this rate does not vary by family income; in contrast, overall 12-month rates are lower among Hispanic women (15%) and white women (10%), but vary by income, with poorer women having substantially greater failure rates than more affluent women.

CONCLUSIONS

Levels of contraceptive failure vary widely by method, as well as by personal and background characteristics. Income's strong influence on contraceptive failure suggests that access barriers and the general disadvantage associated with poverty seriously impede effective contraceptive practice in the United States.

[Clinical analysis of percutaneous balloon mitral valvotomy in 1063 patients]

This article reports the clinical study of 1063 patients who underwent percutaneous balloon mitral valvotomy (PBMV) and 1043 patients among them who did successfully (98.2%). After the procedure, left atrial mena pressure fell from 3.19 +/- 1.06 kPa to 2.00 +/- 0.93 kPa (P < 0.001), mitral pressure gradient decreased from 2.79 +/- 1.20 kPa to 1.33 +/- 1.06 kPa (P < 0.001). Disappearance of diastolic murmur and significant improvement of cardiac function were achieved. Among the 20 failed cases, there were cardiac perforation and/or pericardial tamponade (8 cases), cerebral embolism (3 cases), severe mitral regurgitation (3 cases), atrial septal defect (2 cases) and discontinuance of the procedure due to various causes. The short-term outcome of PBMV is satisfying, so it can replace the surgical closed valvotomy as an effective treatment for selected patients with mitral stenosis.

Dissecting the role of acyltransferase domains of modular polyketide synthases in the choice and stereochemical fate of extender units

Modular polyketide synthases (PKSs), such as the 6-deoxyerythronolide B synthase (DEBS), are large multifunctional enzyme complexes that are organized into modules, where each module carries the domains needed to catalyze the condensation of an extender unit onto a growing polyketide chain. Each module also dictates the stereochemistry of the chiral centers introduced into the backbone during the chain elongation process. Here we used domain mutagenesis to investigate the role of the acyl transferase (AT) domains of individual modules in the choice and stereochemical fate of extender units. Our results indicate that the AT domains of DEBS do not influence epimerization of the (2S)-methylmalonyl-CoA extender units. Hence, stereochemical control of the methyl-branched centers generated by DEBS most likely resides in the ketosynthase (KS) domains of the individual modules. In contrast, several recent studies have demonstrated that extender unit specificity can be altered by AT domain substitution. In some of these examples, the resulting polyketide was produced at considerably lower titers than the corresponding natural product. We analyzed one such attenuated mutant of DEBS, in which the methylmalonyl transferase domain of module 2 was replaced with a malonyl transferase domain. As reported earlier, the resulting PKS produced only small quantities of the expected desmethyl analogue of 6-deoxyerythronolide B. However, when the same hybrid module was placed as the terminal module in a truncated 2-module PKS, it produced nearly normal quantities of the expected desmethyl triketide lactone. These results illustrate the limits to modularity of these multifunctional enzymes. To dissect the role of specific amino acids in controlling AT substrate specificity, we exchanged several segments of amino acids between selected malonyl and methylmalonyl transferases, and found that a short (23-35 amino acid) C-terminal segment present in all AT domains is the principal determinant of their substrate specificity. Interestingly, its length and amino acid sequence vary considerably among the known AT domains. We therefore suggest that the choice of extender units by the PKS modules is influenced by a "hypervariable region", which could be manipulated via combinatorial mutagenesis to generate novel AT domains possessing relaxed or altered substrate specificity.